Rebel if I had a 3:50 in my car and it was in good shape I prolly would put some 28's on it and forget about new gears.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

so i think what you are saying is that i should be fine with power if i want to haul some stuff?

If you are hauling (or towing) and don't need the ground clearance, the 4.0l is a good engine for a lot of applications.

I wouldn't try to tow a 6000 lbs plus load....

However, a could of jet skis on a trailer should be no problem.....

ok, so will i be fine with the stock 3.55 or what? I mean, not only for towing but I'd like to have more power anyways. And I've done a good ammount of stuff to the engine for that.

Rebel All you have done to the engine is to help it to make a little more noise and maybe wear out quicker! Then putting the lift and the big tires on it have slowed down the rpm.. So the engine thinks it is going uphill ...always...never a back slope for that engine.
So now you want more power.
It's gonning to have to be more rpms. The easiest choice would be a set of nice STOCK tires. Twenty six or twenty seven inches would help both your gas milage AND your horsepower..
BUT I'd betcha that simply is NOT gonna happen...is it?
The new small tires would be the best choice in my mind by far.. even a lower price..
Going down to a 3:73 is hardly any difference at all. And in my mind not worth the effort.
Going to a 4:11 would make a noticable difference. And using the 4:56 would be totally out of the question in my mind.
Big Jim <img src="/forums/images/graemlins/pfft.gif" alt="" />

The main downside of lower gears is higher rpm on the hwy, which means more noise, slightly more engine wear, and the possibility of lower mileage (or higher if the gearing isn't right).

I think the key here is to build up your Jeep and particularly your drivetrain as an entire system. In other words, don't just guess at the gearing. Match the gearing to the existing trans, tires, and engine mods. For example, most engine mods move the power band up in the rpm range at the cost of lower rpm torque and so lower gearing is called for. Auto trans requires different engine build than manual and each require different diff gearing

Anyway that's the theory. Pretty sure my solution isn't optimal yet.

I have a 3spd trans, so lower gearing means screaming down the hwy... I opted to restore the original effective gearing for th stock tires by going from 29" tires to 33" tires and 3.31:1 gears to 3.73:1 gears. Kind of high, yes, and hurts power a bit.

So if you have OD it'd be no problem to find lower effective gearing than this without screaming at 75.

For what it's worth, check the gear calculator at http://www.4lo.com/

Also, check out this article on gearing:
http://www.high-impact.net/transmission_and_gear/Systems_Approach.htm

Michael