I am looking at a used 2000 Winnebago Journey diesel pusher with a Cummins 275 hp, and Allison MT643 4-speed transmission with about 6000 miles. I like everything about the motor home, but would like some feedback about the 4-speed transmission and if the 275 cummins is big enough for the 36' motor home. I drove it and it seemed to have good power and acceleration, though the area was fairly level. It was around 1800 RPM's at 60 miles an hour and easily went to well over 70. Would gas mileage be much different with a 5 or 6 speed transmission? I would greatly appreciate any feedback from the great people on this board.