2004 Sportsman 400 Drive issues.

I have a 04 Sportsman 400 that won’t seem to move, if I out it in high and press the gas the engine revs but starts to bog if I continue to push the throttle. I took the belt cover off and it looks like there is a lot of play in the belt. The belt itself is brand new but even installing it seemed a little to easy to get on and off. Any ideas?