I currently have 235-85-17 cooper st's, i want to upgrade to a 33-12.5-17 in a mud terrian, i have a stock 97 f150 with the 4.6 4x4 i know its limited slip, but not sure what the stock gears are.... Would i need to regear to keep decent mpg and not ruining the tranny and other stuff, or can i slide on by?

 

It may or may not be worth re-gearing, depending on what your current ratio is. Since you said you know it's already a LS, It's more then likely 3.55LS. Check your door jamb and post back what the code is. It's probably an H9 which is 3.55LS. Going from 3.55 to a 4.10 ration might not be a bad idea with 33" tires.

 

I agree, 4/10's for 33's. You'll better the mileage with those tires. You don't have to, but it would be noticeably better.

 

you dont have to. im running 33" tires on mine with 3.08 open diff and i still have decent power with my 4.2L. i will regear when i got to 35"s though

 

No need to, I run stock 3.55's with my 35's

 

nah you'll be fine with your 3.55s. its a LSD. i think your money would be much better spent on a set of lockers for your front and rear diff. than on regearing it. i have the same truck and i can tell ya from experience even when im not offroading the LSD diffs just dont cut it. eg, got slightly stuck on a hill the other day on top of the snow, just parking. went to leave and put her in 4 and only two freakin wheels were spinnin. makes me wanna kick my truck. detroit lockers are gonna be my next mod. well maybe after straight pipes hehe