Got a 02 4x4 4.6l with 3.31 in the rear. I am planning on lifting it 4 inch w/suspension and put 35s what would be the best gears to go with in the back when i do all this?

 

you have to do front and back on yours otherwise never use your 4x4. most people go with 4.56 with 35s

 

front and back huh? hmm didnt think of that haha thanks.

 

4.56's

 

i wouldnt have to do anything with drive shaft or tranny would i?

 

No you wouldn't have to do anything with the transmission, transfer case or driveshafts. The only exception is that the driveshafts may need to be lengthened or shimmed depending on how high you lift the truck, though this is usually not needed with a 6" or smaller lift.

From the factory, your truck has X.XX gear ratio front and rear with tires of equal sizes (this allows all of the wheels to turn at the same speed while in 4 wheel drive). If you change out the rear for lower gears (numerically higher) and leave the front alone, your front wheels would be spinning slower than the rears... this would cause you to be spinning the rear tires and using the traction from the front tires to drive the vehicle in theory. In reality however, you will simply start breaking components in the drivetrain as they struggle to compensate for the speed varrience.

A popular gear ratio for 35" tires is 4.56. Since you have 3.31 gears from the factory, swapping to 4.10 gears would give you closer to the same overall ratio that you have now (i.e. your RPM at XX mph will be closer to the same with 4.10's rather than 4.56's). If you wanted to make your truck a little snappier off the line and while accelerating, or give it some better towing characteristics 4.56 would be the way to go. If you really wanted a nice off-roader, and you aren't concerned with your highway mileage 4.88's are an option.

Here is a quick break down for you:
Closest to stock: .................................................. ...................4.10
Better acceleration, good all around: ...........................................4.56
Excellent acceration, great off-raod, not as good on the highway: ....4.88

Precision gear, and Yukon gear are regarded as the best quality ring/pinon for these trucks. Both companies offer all three of the gear ratios that I discussed.

Another thought:
If you ever plan to go larger than 35's, 4.56 or 4.88 are the only gear ratios to consider.