I've never adjusted mine but have had similar problems. I try to, as you do, keep firm downward pressure on the work piece as well as forward pressure to keep it moving at the feed rate. If it does not go through at the set feed rate the drive belt can slip which results in a "snipe" in the middle of the board where the drum is in contact with the wood a little longer, especially if you are trying to take more of a bite than the machine likes. Another very light pass or 2, with constant guidance, usually takes care of it. It would be nice if it just did what it is supposed to do on its own but it definitely needs some help. I mostly use mine for cleaning up old, oxidized, reclaimed stuff-rarely for finish work.