As TrialsRider suggests, the issue could be mechanical. In addition to the great tips he offers, I’d also suggest checking that your rear suspension can move through the full range of motion without hitting anything. A common problem I’ve seen on bikes with aftermarket exhausts is that the new system is incorrectly installed and gets in the way of suspension travel. Stretch or compress the suspension heavily (depending on where the pipe goes) and your swingarm might hit the pipe and suddenly stop, making it impossible for your suspension to keep your tire on the pavement.
Your riding style can also dramatically affect your traction. Especially in corners its important to have steady throttle control and slight acceleration through the corner. This will keep enough weight on the rear and will improve your rear tire traction. There are other things you might unconsciously be doing mid corner (holding too tightly on the bars and preventing them from doin’ their thang, moving around the bike at odd moments, etc.) that can cause small slides. If you haven’t already, I’d highly suggest a couple good riding books, especially ones focused on sport riding. My recommendations in no particular order:
All of these are great books, though I definitely prefer the first two to the third. In the end, I’d really suggest you read them all. The Keith Code “Twist” books are the source for everything, but all the drugs Keith did back in the day messed up his clarity of thought and ability to communicate and teach. His disciples (the authors above) do a better job of not confusing the $%!@ out of you.
Honestly, chances are that you’re not sliding at all. Many things can give you the illusion of sliding when you’re really not. If you’re loose on the bike, smooth on the control inputs, and on the throttle in corners, you’re probably nowhere near a lean angle at which you have to start worrying about that stuff.
Bottom line: check your equipment and think about your riding, but chances are there’s nothing to worry about.