3.55 to 3.73 mileage difference
 

I have an 02 2500 2wd long bed ext. cab, it has a s475 over an hx40 "60-65" with 4" exhaust, banks intercooler, banks 3 1/2 high ram, 150hp ddp injectors, quadzilla adrenaline with pulse, tunnel ram, hotrod vp44, 6" afe filter. That's all I can think of right now but I have 3.55's now and get like 23 mpg at 80 at like 2250 rpm. I tow a 10k 16' v nose enclosed trailer kind of regularly and a 37' 5th wheel rv occasinally. Now I know this is a lot at once but I am kind of tired of the auto and have a nv4500 sitting in the garage which I want to install and goto 3.73's. How will my fuel mileage be affected? And also I don't have the stock 245's I went to 265's. any help will be much appreciated.

probably drop a couple mpgs...

also the nv4500 has a big rpm gap between 3rd and 4th gear that you probably aren't going to like when towing..

another thing: final drive ration between the auto and nv4500 are a lot different so even with the same rear end ratio, you are going to increase your rpm to maintain the same speeds.

im not familiar with dodges but i drove a mid 90s 6.5td nv4500 (think it had 4.10) loved it. now the nv4500 on gm was geared a little different
Gm Dodge
6.34 5.61
3.44 3.04
1.71 1.67
1.00 1.00
0.73 0.75
never had a problem between 3rd and 4th
the 47rh and e i think where
1st: 2.45
2nd: 1.45
3rd: 1.00
4th: 0.69
so a little taller ratio for fourth but it will only put you like said a couple hundred over what your running now. the up side it will be easier to take off and that will affect your mpgs

Yea, well looking at it if I keep the 3.55's and the nv4500 has a taller OD it should even out correct? Bc I lost a mpg or 2 when I went to the 265's from 245's, also the s475 is just about ready to go on the highway, maybe the gear change of the nv4500 will get me into it and save mileage

shorter not taller :tu:

1:1 = direct drive
anything less than 1 is overdrive. like .75 and .69

my old Z28 had a double overdrive 6-spd trans...4th was 1:1 5th was .75:1 and 6th was .50:1

.69 = a taller gear. like longer legs...it can run faster.
.75 is a shorter gear so shorter legs...can't run as fast...so higher rpm to run the same speed as the one with longer legs...

same goes for rear axle ratios...4.10 = short legs... 3.55 = long legs. lower the number, the faster the top speed. higher the number, the slower the top speed and shorter the gear...

anyway, the change should bring you closer to your goal.

worst case you can go to 3.73 (costs an arm and a leg to change axle ratios on 4x4 HD trucks but not as much as the jump from 3.55 to 4.10 with a D80)

lol i got my trans mixed up i was thinking the nv4500 had the .69. then i corrected my self with out knowing. but anyway, i would swap the nv4500 and see how you like it. with being a stick and having the shorter take off gears you might do better taking off anyway. and the 3.73 would just be over kill.