What gears should I get with my new 05' CTD 4x4 AUTO? I tow a 4k lb. enclosed cargo trailer almost everyday and will be getting either 33" or 35" tires. I am undicided on the gear ratio, because I still want all the power and fuel milage after I install the larger tires. I do know of the poor fuel milage a diesel gets with 4:10's, but will it be a better combo? I average 40 hwy/60 city. This will be my first diesel and I want this truck "perfect".

 

You will get about the same mileage with a 4.10 as a 3.73 until you go over 60 mph. You really need to consider the larger tires. If you go to 35" tires I would opt for the 4.10.

 

I am undicided on the gear ratio, because I still want all the power and fuel milage after I install the larger tires

A little confusing, but overall I agree with fiverbob. I spend most of my time at highway speeds, so I'd rather have a 3.55 anyway.

 

I do not tow much--just a popup camper--1700 lbs with 2 four wheelers on a trailer. My 3.73 has an incredible amount of power compared to my 350 chevy.
I have pulled a seven mile grade (I am guessing about 5%) into a stiff wind and maintained a steady 65 in sixth gear.

My cousin bought an 04 4.10 dually 2wd to replace his old V10. He is a full time rv'er and pulls a 14k fifth wheel. He tells me he thinks he made a mistake, and feels the 3.73 still would have adequate power for his needs and better mileage.
Towing only 4K should be a breeze with 3.73.

 

My neighbor pulls about 7k.He has a 05 dually with 3.73.He says it was a mistake.Should have got 4.10s.Gearing with the auto is just a bit too tall for mountains.Stays in the pedal hard then it downshifts and screams unless he's at 70 plus mph. 4.10s would have lowered that speed and given more grunt.He was hoping to get a shorter tire but none made.With TALLER tires 4.10s would be the way to go.

 

If you go to the taller tires, you will lose a little mpg and a little grunt. I did anyways.....

 

Larger tires = 4.10 gears.

 

I had 4:10's, 35" tires and auto on my last rig. I tow frequently. I hated the 4:10 grears with this combo. It would probably be OK if you had a manual tranny because you can controll the rpm's. But with 4:10's the auto trans is always "searching" at a certain grade while towing. Here is an example that happened every time I towed: Driving up hill at about 45 mph, transmission would shift to 3 rd when I really needed the extra rpm's in 2nd. I would hammer the throttle to frorce it into 2 but within 1 second it would shift back into 3rd. In 3rd gear, the truck slows way down, rpm's go down (decreased power) and truck gets hot . This is w/ OD locked out of course.

My current rig has auto, 35" tires and 3:73 gears and I don't have the problem. Same trailer, same route, less searching. The trans will still search but at about 10+ mph faster - 55 - 60 mph. I think this is fine while towing.

I have noticed many folks think you need the 4:10 gears for towing because they say you need the extra "power". I have learned from persoanl experience that these engines have plenty of power to tow with 35" tires. The problem is not lack of power but poor programing. You can get around the poor programing with the 3:73 gears. It doesn't hurt to turn the duration box to 1 and the EZ to 3 - with this set-up, I can do almost any grade at 60+ mph and have reasonable EGT's. This was not possible with my 4:10 gears.

 

go for the 3.73 the truck still has plenty of power to push tthe tires as well as pull the trailor. I pull a 30ft gooseneck loaded with gvw at 18755# with 3.73 and do it with no problem. You'll like the mpg on the 3.73 much better, considering fuel prices are on the rise.... 2.39$ in Cincinnati

 

Well, considering I'm currently regearing, you have to ask yourself a few questions. If you're going to bomb, and stay at small tires, I'd go with 3.73. 3.73's, 35's, and 400whp gets you 17.5mpg unloaded on the highway. Since I plan to go to 37s in May, I'm having 4.11 gears put in.

 

I got an improvement when I went to 285 tires. If you drive the truck with bigger tires and try to get the same acceleration as you normally do, you will get worse fuel economy as you have to give it more fuel to overcome the new gearing.

Make sure you also get the speedo changed, as you won't see an improvement if you don't.

I hope your getting new control arms and a lift when you put those 37's on. I have been driving a crew cab long box with 37 in. BFG's for awhile now and they definitely will hurt the turning radius because of the rubbing on the control arm.

My notes from 37's:

Decrease in city driving fuel economy due to increased rolling resistance of the big footprint these tires have (14mpg). Increase in highway mileage though, steady state over several hundred miles gives 20mpg avg. if you keep it at 70-75. Plus the traction is amazing.

The truck has G56/3.73

 

I tow my 5-6,000lb work trailer about 75% of the time. I have the 3.73 and like it. But I have stock sized tires. If I had the 4.10, I'd have to shift faster than I do already.

 

towing 4,000 lbs, I would go with the 373. I tow 9,000 lbs and the truck doesn't know its back there I am going to put 315's on my rig....and i'm not woried a bit.

BTW, i have 373

 

If you are going 35-37 tall tires you had best get the 4:10's.

 

I towed 12,000lb boat trailer with my 99 with 3.55's and 285's with no problem, again it was modified and seemed to out accelerate my 05 (which is stock for now).

I wish I could get a 3.08 rear gear. If I wanted to go fast I'd get a procharged 8.1L.

Plus, then I could do 85 at about 1800 rpm getting 24mpg.