2.01 Software, V1 Axon performance

Just updated our 2 Axons (Pentium Mboards) to the new software (2.0.1). Seems to work ok until I dial up an HD clip, then it just falls on its face. The first second or 2 of the clip plays wonderfully, then it starts stuttering and jerking, and finally drops off to a frame every few seconds. I've found that at about 20 frames per second (according the hog) it seems to play smoothly.

All this is on content that had played smoothly on 1.5.1. The particular clip I'm looking at had been encoded to Axon/DL specs a few years ago and has been resident on the machine ever since. Any suggestions aside from upgrading to a new axon or dropping the resolution?