If you're going to be running larger-than-stock tires, especially with larger tires, you'll want a heavier duty clutch than stock. I went all the way and got the centerforce dual friction (run it in two of my vehicles). Pedal pressure is identicle to stock. I run 33's on one vehicle and 35's on the other. Larger tires require letting out the clutch pedal more slowly.

Your symptoms of spinning under hard acceleration do sound like the clutch is going.

If/when you do a clutch, make sure to get the pilot bearing, throughout bearing, pressure plate, clutch disk, and alignment tool. Most clutch kits do not come with both bearings, so make sure to ask. Also plan on having the flywheel resurfaced (around $30). If you don't and the surface is damaged from the slipping, it will wreck the new clutch. Now is also a good time to replace the shifter bushing on the transmission stick and check for oil leaks from the shifter housings on the t-case and transmission, rear output shaft seal, and front input shaft seal, and engine rear main seal. While this sounds like a lot of extra work, it isn't. And you don't want to have to go back in there later for a $10 seal....