How many cuts do you have? (You can check this by holding both the forward/backward buttons while powering on the machine, getting you into maintenance mode).
If you have less than 1,000,000 cuts, I would try cleaning the wheels with a good solvent first. We ran into this quite early on because we would trim label stock. The adhesive built up on the blade and made all of our cuts look like the blade was dull. We only had ~300,000 cuts so it was not even near needing to be sharpened though. A good clean fixed us right up.