I have been running 32x11.5x15 on my 2000 (which is more similiar to your 98) and just recently put on OME HD shocks all around and turned the torsion bars a little to level out the ride. I am looking at converting to 16" wheels and going with 255/85. This will give me a 33.5" tire with a width of about 10". Not sure when I will get to this (read wife approval), but the 32" fit without any lift and since I did do the OME suspension it gave me enough of a lift that there is a lot of day light in the wheel wells so I think that 33" will fit fine. The OME suspension was the best thing I ever did to the truck. The rear got the new shocks and springs and the front I only upgraded the shocks as I do not plan on a winch/bumper. The ride is very smooth loaded or with only me. My only concern with going to 33's is the ability to climb on the trails as I too live in Colorado and some of the trails can require more gearing than what we have stock (on big wheels).

Good luck!