I think you only have to modify the dual piston calipers which came on newer models IIRC. I had 15 x 10s on mine, and didnt have to modify anything...but not sure how much back spacing they had though

 

I heard that '96 was the last year you could run 15" wheels. As far as size 33s will fit it was width where I had, and still have, trouble with. My side lugs have hit the control arms ever since I got 33s and continue now that I have 35s and a level lift but it only makes a little damage to the tire and doesn't hurt my turning radius too much. I'm sure you could live with it but I would sugest the 2500 calipers if you plan on running larger tires

 

I think 15" wheels will 'fit' up to the 99 year trucks. In 2000, they went to the dual piston calipers, and there isn't room for them in the smaller wheels.

 

I also don't think they'll fit any 2500 caliper.

 

Generally...

255/85/16" = 33" x 10.5" x 16" tires
285/75/16" = 33" x 11.5" x 16" tires
305/70/16" (notice it's 70 not 75) = 33" x 12.5" x 16" tires.

And they'll rarely measure out to a full 33".

I'm running the 285's on 16x8" rims with a 2" lift front and rear, and it looks nice. And with just a 2" lift you don't have to worry about the front trackbar. Here's a picture: http://www.jeepforum.com/forum/f27/e...l#post19568457

 

I run 15x8 steels on my 97 and they clear fine. I also have the 7500gvw "light duty" 2500 calipers which have a larger piston, again no issues. From the looks of it 15x10s would work just fine. As always heed caution and try before you buy if you are able.