When you say the auger plugs, what do you mean? If I put too much in the 336, first the auger moves to the top of its float travel and bangs on the stop, then if too much beyond that it stalls out.
Usually the cause for me is running pickup too low and it hits the ground stalling the teeth which plows up a big chunk of windrow as I drive that gets sucked in as one big blob plugging the auger.
I did have to adjust my belt tensions or something when I first got it years ago. I also had to fix teeth and sheet metal on the far side of pickup that hay gets fetched up in.