On a 2009 GU 813 Iam having a little trouble with the allison transmission, not always, the problem just comes and goes intermittently. Sometimes when I start the engine, select D, add gas the trucks moves but you feel instantly a rough feeling (like if you have selected LOW in a 4x4, it kind off jumps), and the next gear takes a long time and the engine starts rev up and the gear enters with a very rough movement and so on the next gears, but if you stop the engine and start it two, three or four times and it is all gone…. it has never been the other way around, if you start the engine for the first time and no roughness it continues ok for the rest of the trip. There are no codes on the gear case. I've heard it can be air in the fuel system is this possible or should be looking at something else? thanks!!