Need advise

I recently purchased a 2007 TX model. It has 1906 hours on the hour meter. Engine runs good. But it has a bad clunk when putting it in gear. It seems as if there is a lot of slack in the drive train. After gently pressing the accelerator it then goes good, no noise. The belt seems to be loose. Can this cause the problem ? Some times after engaging the gear it will lurch, clunk and then go.
This is my first gator and am not sure that this is normal.
If slack in the drive train, is there a way to tighten it up ?
Thanks in advance, Jerry