bluebull

Leave it in t/h mode all the time. truck should load manage on it's own.

bluebull

If your truck is unlocking instead of down shifting there's something wrong. Either a reflash or something in the transmission is need looking at.

Auto, 3:73, locked up in OD at 65 MPH should be around 1800 RPM's. Same conditions locked up in 3rd should be around 2600 RPM's. If your running 2300 RPM's then I would say the converters not locked and needs to back to the dealership for diagnostics.

SBishop

I agree with Bluebill. I have ran in 3rd gear lock up all day into headwinds and still get 11-12mpg. But of course I have the wimpy 250hp with the ole so lame 47RE

And I only have over 90,000 miles trouble free

roadgeneral

I've said it before, but.................in general, horsepower costs mileage. These '06 325/610 CR CTDs w/48RE tranny just don't get the mileage that the older models do. I have seen 19 mpg on my overhead, but it's actually about 17 mpg when hand-calculated unloaded on the Interstate at 65 mph.
I only have 8500 miles on mine, so maybe it's not broken in yet. I have not talked to anyone who is getting high-teens or low twentys with these 06s.

Lost Lake

When my truck starts to slow on a hill, the TC unlocks, and kicks into third unlocked, then it locks up in third after a few seconds. It will stay in third for miles and miles at around 2300 rpm.

I am running 2000 rpm at 72 in OD, and 2000 rpm at about 55ish in third. So yeah, I think it's around 2300 rpm at 65 or 68 or whatever. Either way, it's sucking fuel like crazy.

Yesterday I drove down to Pigeon Forge, TN and I took the back roads running between 65 and 60 without the cruise. I would let the truck roll up to 70 on a good downhill run, then fall off to 55 uphills just keeping a light foot so it wouldn't kick out of OD. My optimistic mileage monitor was reading 12mpg on that run, verses the 8mpg it read previously.

The few times I couldn't stay in OD on long uphill grades and had to drop into third the OMM fell quickly!

paul4romtexas

I pull my boat, about 4000 lbs, all over Texas just about every weekend. Went 700 miles roundtrip last weekend and averaged about 14 mpg. The truck has just under 20,000 miles on it. First of all, your truck is not broken in at all at 5000 miles. You will notice a HUGE difference when you break the truck in more. Also, keep your tires aired up, that makes a huge difference as well. I have never noticed any unlocking or downshifting. I dont use tow/haul mode, I just put the cruise control on 70 and sit back and listen to music. Never had any issues and although I would love better mileage, I am happy with 14-15, especially since all my gasser buddies get about 10 mpg with their boats. I would just say keep pulling weight and your mileage will get better and watch your tire pressure.

rustyshakelford

what kind of boat do you have?

brett

paul4romtexas

bass boat, tandem axle trailer

*typo on the 6000, just shy of 4000 with the trailer and equipment

WA4SLC

I am pulling a 10,000 lb. travel trailer with my 04.5 and my mileage is usualy 10.5 running 65 mph on the interstate in od. I have the Quad XZT and an AFE proguard 7. I just from a trip to Charlotte and I got 10.8. You can see from my information bellow that I have 4:10 gears and an automatic. I have about 33000 miles on my truck now. I use it mostly to tow the camper and run a few short trips that I need a truck for. I get a little over 19 mpg at 70 mph with just the truck.
I am making a trip to Branson MO in July to attend the iRV2.com national rv rally and I am estimating that it will take between $600 and $700 in diesel to get there and back. That is more than the camping and all of the extra cost events will cost. That really hurts. I would really like to get mine up to at least 13 mpg, that would help some.

Bill

stezlaki

We went to Colorado (~1800 miles one way) over Christmas when my truck had about 3500 miles on it. We were towing a 24' enclosed (square front) trailer, probably about 10,000 pounds loaded. Mileage was about 9.3 or so running 85-90 mph, and about 10-10.5 going 75-80. Weird thing is mileage didn't really change coming back empty (~5900# trailer). Transmission stayed in tow/haul mode and NEVER downshifted/unlocked unless I floored it. This was with a Bully Dog on the tow (lowest) setting.

Here's the interesting thing. My around town mileage (truck only) is also only in the low 10's and the best I've ever gotten (again, truck only) is in the 14's on the highway. Maybe it's just me, but it's amazing to me that I can get the same mileage towing 10,000# at 75-80 mph as I can driving just the truck back and forth to work at 30-50 mph!

My overhead is pretty consistently 2+ mpg optimistic, but the above #'s are hand calculated.

davelinde

I just got back from a 2200 mile round trip towing 10,000# FW.

Wind makes a big difference but I've never seen less than 11 mpg with typical closer to 12 (calculated). 7mpg just sounds wrong to me... worth looking into it.

I've got the 3.73's and pretty much follow the speed limits... 60 and 65, occasionally 70. Typically 65.

06megacabman

Lost Lake
Your description sounds exactly like what I experienced over Spring Break. I have an 06 Mega 3500 with Proguard 7 and torque tube. Truck was loaded with family/quad and pulling a Toy Hauler weighed on the scale at 10,650lbs. Was probably ~20K total truck and trailer. Doing 60-70 on the freeway in Tow/haul mode. On hills the truck would shift down and the rpms would jump to about ~2500 rpm. after leveling out over the top I would have to let up on the gas peddle to get the truck to shift up and get the rpm's from 2500 back to 1800/1900 in 4th. Seemed like if I could get it up to 65-70 without pushing the pedal too hard or not too much incline it would shift up (RPM down) on its own otherwise I was letting up on the peddle all the time. BTW when I got home my overhead showed 9.8mpg average doing 65-70 most the way home.

Now I'm new to this so if someone could tell me how I can tell when the TC is engaged vs. not engaged I would greatly appreciate it. I thought in T/H mode the TC is locked from about 45mph and up.

roadgeneral

What you have descibed is normal. Those of us with '06s have experienced the same thing. The ECU not only senses road speed, but also throttle position. through the TPS. Under normal conditions it will give you TC lock-up in 4th gear (OD) above 45 mph. However, when you are pulling or into the throttle, it will not make the shift until you lift your right foot a little. How do you like that 4th to 3rd down-shift under a load? That scared the crap out of me the first time it did that. The RPMs went way up before finally settling into 3rd gear. That is said to be normal. It's supposed to cushion the load from the engine to the tranny. Too much torque with the diesel. Since I experienced that shift, I have been manually pulling it down into 3rd after lifting off the throttle. Works for me.

Lost Lake

I don't mean any disrespect, but a 4,000 pound boat is really absolutely nothing compared to a 10,000 pound fifth wheel that is over 11 feet high and has a flat frontal area of almost 80 square feet. And my Mega weighs in at 8400lbs with just the family and fuel in it. So realistically, we are tallking 19,000 pounds rolling with a drag like a parachute.

I can get 11mpg if I keep the cruise off, but that delayed shift into OD is killing mileage. It will stay in third for MILES on a flat level surface. And I am running my tires at 85psi.

The new 305's go on in two days, that will change everything!

06megacabman

Was real concerned the first time. I have a boost gauge and between that and running about 500 below redline I got concerned. Also wasn't sure about the water temp. Seems to jump to about 205/210 or so climbing when in 3rd.

Misery loves company.