Thanks for the info and advice. We have tried fuel filters, and air filters, to no avail. Not sure on the boost pressure. We definitely do not get 125% before engine rpm loss. We probably only get about 108-110%, and then rpm goes down fast. At 125% we would be close to plugging. The dealer was out and checked everything with a laptop, but I wasn't in the combine at the time, so am not sure what the readings were. We are done harvest now, and the combine will be going in to the dealer soon, so hopefully we can get it sorted out.