my 13-inch thickness planer was "skipping" as it fed thru a 12-inch maple plank; each stop-point had a crosswise divot, too deep to sand away.
Took apart the left end (where the roller-drive chains are) and found that the outfeed roller's bearing block was toasted -- had worn into oblong shape and caused the roller to jump every few revolutions. Ordered a replacement and re-assembled with the block rotated 180. The darn thing ran right and I finished the job.
Don't be afraid to mechanic yer toys.
JRHannum