Body lifts arent really the best way to do things in my opinion, but it might help the job out. I run a 3" body lift on my truck, and if it werent for that, Im sure my tires would rub a lot worse than they do now.
As for the gears... *deep breath & sigh*
Everyone is going to have a different opinion on how their truck drives, everyones engine is going to make different power, everyones engine is going to be at a different level of repair/tune/freshness, everyones truck has a different amount of crap in it/on it/built into it, so theyre all going to weigh different amounts, etc. Therefor, everyone will have a different opinion on if they need the gears or not.
NOW THEN, my personal opinion is this... Dont waste any money on the damn gears yet! IF, IF you decide to actually cram some 33s under the truck, it will feel sluggish compared to the stock tires, however, how much depends on the vairables listed above, along with tire weight, wheel weight, tire pressure, blah blah blah.
Getting gears for however much per set, then having them installed for however much is going to be a large cost if you dont do it yourself. Randys quoted me almost $500 PER DIFF for no lockers (I eventually just did the diffs myself after sourcing out the parts and doing lots of research). THEN, if by chance you DO SAS the truck, you CANT EVEN RE-USE THE FRONT DIFF! Now you have to have ANOTHER diff setup with gears to match the rear, but by this time, if youre going to run larger tires since youre doing the SAS, you are gonna want a DIFFERENT ratio, so now BOTH diffs have to be redone. Notice I didnt even mention any lockers in that example?
Plain and simple, its just turd polishing to throw money at an IFS truck if you even THINK that youre going to want more than IFS someday. Just my opinion though.
~T.J.