Kenworth t680 transmission problems

Does anyone have any ideas why my transmission is acting up? I have an ultrashift eaton transmission and every now and then is having some issues when downshifting while jake brake is active. Lets say I'm going downhill, jake brake is on and I make a downshif manually. It is supposed to go on the lower gear and engage the jake brake, but instead it jumps in neutral, then rpm goes up, trying to find the correct gear and after the jake brake is engaged. The other day I got stuck in 3rd gear without being able to do any upshift or downshits. After turning the truck of and on, everything went back to normal.