Quote Originally Posted by BigRabbitMan
......I am not quite sure why some relatively straight forward questions such as normal rpm at 65 mph are going unanswered.

Thank you for your interest,


It's not straight forward. Your MH will have a drive ratio unique the the MH. Very different than the vast majority discussed here. Your RPMs will be the same in direct (Allison 4th gear), regardless of the tranny. The 5/6 speed Allisons will have an OD of .71 in 5th, and .61 in 6th. Just do some math (or ask for help with it) and compare it to what you have. Unless you plan on changing the tire size and/or drive ratio, it will be the same, with an addition of OD(s). A 6 speed may not be the best answer if you have no OD now. If you have a 70's era auto tranny (TH400?), it will have a direct final gear. Adding any OD will be a bonus, and a lockup converter won't hurt, either. With the weight you are dealing with, a double OD won't help unless you have a deep enough final drive ratio.