Clearaudio Performance DC issue

I have a Clearaudio  PerformanceDC table, Tracer tonearm, Ortofon Cadenza bronze cartridge with a chronic issue. I know nothing about setting up turntables, but this one has been set up three different times by dealers who do. At first it sounds great. After a few hours of play I notice it begins to distort and then-for no apparent reason-the tonearm will just skate along the record. This has happened three different times after being set up by folks who I think know what they are doing. The dealer is not local and at this point I'm not getting much help on that front. Out of warranty. 

Before I ditch this thing, just wondering if anyone has had a similar experience or any ideas. Its frustrating, because when it works, it sounds great.

Thanks.