i have a 2013 with 3:55's, if i want to change to 3:73 or 4:10, can i just switch the gears or do i have to change the diffs as well?

 

you can just change the ring and pinion gear as long as your bearings and seals are in good shape... normally one size gear change isn't gonna be significant to justify a gear swap due to cost.

if you're 4wd, you obviously have to do both... did you up your tire size? if so divide your new tire size by your old tire size and multiply by your current gear to get back to stock... most people go one size taller (lower gear higher in ratio) to make up for the loss of power specifically dealing with your new heavier and likely wider tire's increased rolling resistance ex 35/32*3.55 = 3.88 (which doesn't exist but if your 2wd 3.90's do either way most would go with 4.10's to get the stock feeling)

 

added a 6" lift with 35" tires on 20" rims

thanks for the info, since the upgrades, the truck feels like a 17' bass boat towing a 300' container ship! :P

 

Is it a new engine selection? Shouldn't be that bad unless it's like a 4.6 or something.

 

5.0

 

that makes sense... don't know if you've tried this already but I think with the 6speed trans, I'd get a tuner to recalibrate the speedo and trans shift points first. that first gear is pretty low to begin with and after that if your truck doesn't shift into 6th until 65 who cares as long as the overall gear ratio from the engine to the tires is correct and you end up being in the proper rpm range and riding in 5th mostly... It's just a cheaper option to start with if you havent already and you'll kind of need it IMO with a gear swap and those tires anyways.

 

If you're going to do it, go to the 4.10s. The 3.73 isn't enough of a change to justify the expense.