I have 4.10's and 33x12.50's with a NV4500. I have gotten mine up to 98 MPH one night when I had an emergency. That speed was by GPS too. Had my two dogs in the truck and they didnt like it at all. I wasnt watching speed and just noticed bad vibrations and loose steering. When I looked at the GPS i quickly let off the throttle. Mine would only run about 83 until I destroyed the old transmission, but I think that was due to what ever was going wrong with it. When it would hit about 83 it would sound like the clutch was slipping and the motor would just rev. This top speed was with the New Improved NV 4500 that feels alot better than the other one.

 

Unless you're towing 20K+, 3.54 gears are just fine. If you dont like how it pulls, do some minor tuning. Personally, I think 4.10s are just good for wasting fuel and not much else. I've pulled 22K GCVW with 3.54s at 65mph, and averaged 12-14mpg going from KS to CO.

With your mechanical background, you'd only be out the cost of the gears and a day setting them up. I think it'd be more cost effective, easier, and have fewer things to worry about vs an OD unit.

IIRC, with 235/85-16s in my 91 (4.10, 5spd), 70mph was right at 2400rpm. 80 was getting close to 3000. Still got 21mpg with it.

 

I figured mine at about 22 mpg at 70mph (easy driving) on a 130 mile trip..... 150 total with 20 being just getting out of Dallas.

 

crossy's son - thanks for the correction, I thought that the spring simply raised "red line" from 2800 to 3200.

92roughstock - when you say "fewer thing to worry about with an OD unit" are they known for causing issues, or you simply mean it will be one more set of moving pieces that "could" break. I currently love the reliability of my truck and wouldn't want to risk any of it.

 

i feel your pain. i blew up my 3.07 rear end and was running 3.54s with a 727 3-speed for months. 2300rpm at 55 with 265/75r16 tires

5-speed here i come

 

The Getrag G360 has 0.77:1 overdrive and the NV4500 has 0.74:1 overdrive. Using the stock governor spring in the VE I don't know of any reason you couldn't "mat" the throttle and run on the governor assuming the speed limit isn't exceeded. I'm running 3:54 with the A518, 3200 rpm spring and have never seen it on the governor in overdrive. I have however seen 90 mph.

 

Someone that is better at the math than I should check this but I get 87 mph calculated speed running 285-70-17's, 4:10 rear, 0.74 fifth gear ratio and 2700 rpm. And at 2500 rpm top speed is about 80 mph. Sounds like you are defueling.

 

3200 spring will give you more fuel at high rpms, so your engine will sound "right" @ 80. Just for comparison, I put mine in and tested it w/o O/D. My engine used to scream at 70 MPH with the old spring, with the new it's like it's saying "is that all you got?" I could probably get 80 easily, but it sounds kinda scary to rev it up that high.

 

I can run over 70 in 4th gear with my 93 which has 4.10's. As said above get the rpm's up ( All I did was take out the high idle screw ). I can go way faster in 5th than I want to drive. I like the 4.10's. Maybe If all I did was drive on the interstate I would want something different. I would like a G/V overdrive though.

 

As long as the road/ or track is good for the speed they aren't too bad in the triple digits. If your suspension is in top shape that is........

 

according to the rpm calculator I use that sounds about right.

 

so the fact that i cant "mat" the throttle pedal while on the freeway in fifth without the truck sounding weird, does kinda point to there being a de-fueling problem?

i would like to fix the problem of not being able to drive with the flow of traffic, if it is a problem, but even more so I would like to fix any actual problems with my truck before they become a bigger issue, if there is one.

 

Most of that weird feeling is your brain telling you that the pedal is all the way down and your not gaining speed. If you increase the high idle speed ( wide open throttle ) then you will get rid of that feeling. My 89 with 3.07's and a 3 speed is about the same final drive ratio as a 4.10 equipped truck with a overdrive. It would do 75 to 77 mph flat out. It felt the engine was just running out of steam. ( due to the gov. it actually was. ) That same truck with the stock 386 gov spring and the high idle screw gone will do around 95 or so. It really gives a different feel. Now at that 75 mph speed the truck is still pulling hard.

 

By "fewer things to worry about," I meant, one less thing that "COULD" go wrong (which it will, at the most inopportune moment imaginable). New gears should cost way less than $500 (assuming you dont have to do a complete rebuild), vs $3000 for an Od unit.

One other thing that could give that weird sound is if your lift pump isnt keeping up with demand, it will tend to defuel, and may actually be trying to cavitate the pump at higher RPM and load. Stick a fuel pressure gauge on there and take her for a spin. Cummins calls for no less than 3psi at all times. Personally, I like to see 5 or better.

 

I'll look into getting a fuel guage that i can check pressure with, if pressure check out ok, I'll be messing with the high idle screw. thanks for all the input so far everyone.