31's Or 33's
 

I am buying new tires soon and was wondering if I do a body lift and put 33's on my truck, if it will affect my power much.Its a 3.9 so I know its not a power house or anything.I just don't want to spend $1000 on tires and my truck barely pull after I put them on.

Figure a 33 is 10% taller than a 31 (almost) so you will feel 10% less seat of the pants power if you go with them - If however your stock tires are smaller than 31 I wouldn't recommend it at all. At least not w/o a re-gear which is crazy expensive in my book.

You already know the taller the tire the worse the power - an automatic will help some with that if they are kind of close to stock -

For example - I had a 4cyl 1995 jeep YJ & the stock tires were like 26 inches - I moved up to 30's & could barely get it to move. Couldn't reach 65mph on the highway at all.

Now I also had a 91 YJ with the 6cyl & I was able to put on 31's w/o noticing any difference at all - mostly because the 6cyl had much more torque.

In general you can go 10% over stock w/o noticing much difference - beyond that & things get sketchy.

33's wont be to much of a problem with the 3.9.

Haha, you had 30's on your YJ and you couldn't get to 65 midget?? WTF, you must have had a worn out YJ because i had 32's on both my YJ and TJ and could still use 5th gear and pull 75 easily down the interstate all day. And yes I had the 4 cyl 2.5. Don't even worry about 33's on that 3.9. They are underestimated, I think they have PLENTY of power compared to other v-6's (chevy, ford, toyota) My friend has a s-10 with a 3 inch body lift with 32" nokian vativa M/T's and that things not even a dog, (I'll admit it eventhough I hate GM) so if that thing can turn em with that small ass v-6 I know our 3.9 can spin em with NO PROBLEM.

EDIT: I just noticed you have a 5 speed, I also had 5 speeds in my Jeeps, so you won't have a problem, no way!

My buddy has a 4cyl 5speed wrangle with 33's its not the fastest but can pull 70 alright