How many kms on the sled? I'm no clutching guru either, but I've picked at it a bit.
A couple things might be going on in either the primary or secondary, from bad rollers, springs, or even ramps in your primary. If you haven't done any maintenance on the sled since you got it, it is probably time to have them looked at anyway for peace of mind and preventative maintenance at the very least.
One thing you may be able to try is adjusting the pins in your primary. People often refer to them as clickers. Their position changes the RPMs that your clutches can acheive and you are albe to basically dial in your desired RPM for the conditions you are in. There is a product called Quick Clickers that make this easy to do on the fly, but it shouldn't take more than a 10mm wrench if you don't have them. Your maintenance manual should give a decent explanation on how to go about making the changes.
Another thing to do is ensure your belt is adjusted correctly. Typically the correct height for the belt in the secondary is that the bottom of the cogs/valley on the top of belt is flush with the outside of the secondary. Your manual should also give the proper procedure on how to adjust this as well. One thing I always get fooled up in is which way to turn the big nut on the secondary, it is opposite than what I consider is the logical way to turn to get the adjustment I want. Pretty much gets me every time...
Having said that, if this is something that has happened recently and your driving conditions haven't changed, chances are that it is an internal component that needs to be addressed.