Sancat11,
I have a 40' 01 American Dream with ISC350 and Pac brake. It sounds like your PacBrake is freezing up, probably because it has not been adequately lubed. I had a problem about 4 years ago where the PacBrake locked up and engine lost power. Finally freed it up and went to Cummins/Spartan dealer and had it replaced. Since then, I have used the high temp lube sold by PacBrake every 6 months or so and never had another problem. Suggest you call PacBrake, obtain their hi temp lube and verify with them condition of brake. Thereafter make sure that brake is lubed regularly. Good luck.
Mel Silverstein