If you have 3.55s, bumping to a 3.92 isn't really that much gain for the cost. You'd be better off going to a 4.10. 4.56s are often used for trucks with 35" tires or a little bigger.

 

Depends how much highway driving he does. I have 4.10's and absolutely HATE them! I wish I had 3.55's

 

i got the 8.25 rear end, at 3.92, i want a better ratio for towing/hauling.. any ideas, i was thinking 4.56

 

It all depends on what you use the truck for city driving or hauling and also on what gas mileage you want or if you can get good gas mileage considering how you use the truck.

No simple answer and not cheap to fix if you get it wrong.

I have the 3.55 with the 2.5 engine geared for gas economy and it works out great most of the time but it would be nice to have a little more guts/power to it and would like to change just a small amount to a 3.72 or 3.92 the 3.92 would be the best for more power but the 3.72 could be the best answer for both a small power boost and keep my good gas mileage

I do also have taller tires than the stock tires not much taller but enough to bog down my engine at times

 

I personally think going up (or down) one step in ratio isn't worth the cost, especially if you've got 4WD. I went from 3.55 to 4.10 on my V8 AWD and I'm so glad I didn't go for the 3.92. The difference between 3.55 and 3.92 is 10% where as 3.55 to 4.10 is 15%.

At 70mph, the engine went from 2100rpm to 2400rpm with the new gears. I didn't think that it would make much of a difference to the highway use but it was quite noticable. Luckerly, my truck has the 45RFE tranny which I decided to try reprogram by using a 545RFE controller off a 05 Grand Cherokee. Despite throwing a code about some "incompatibility issue" and putting all the PNR21 lights on at once, it works! I gained an extra overdrive gear that drops the RPM back down to same RPM it used to run with the old gears.

The extra acceleration is VERY noticeable and the extra torque is very useful when towing my 4000 pound caravan. MPG has improved (not by much, but better than nothing!) around town and has remained the same on the long runs.

Unfortunately, I think you'll already have the 545RFE tranny, so won't be able to anything about the rise in highway RPM. As everyone has said so far, it really depends on what you use it for.

 

I'm glad to see that someone else did the TCM swap. That extra OD gear is really nice when your hauling *** down the interstate.

 

my shop will not warranty non-stock parts. but WILL warranty labor. somthing to think about. but not all shops do it the same. what i didnt like doing my own work is that i had to do my own rework. course didnt we all.

 

Damn, sounds like a bunch of work. It's either drop the 4x4 and swap in a front end from a 2wd, or spend twice the money.. I think I'll just leave it at this point. It would be used mostly for highway/backroads driving back and forth from school. I'll just leave the 3.55s in there for now.

 

If you're ok with not having 4WD any more, you can just pull the front driveshaft out. You don't need to actually replace the front end with one from a 2WD. That way, if you decide to change the front to match the rear at a later time, you can put the front driveshaft back in and have 4WD again. It's pretty common to change them one at a time. You just have to remember, you CANNOT use 4WD with two different axle ratios!

 

Man, I'm running 33's with 3:55's and in o/d at 75mph I'm doing 2000rpm.

It's way too low. When I swap I'm going 4:56.