If the engine is getting up to speed, the governor in the transmission is the accepted item to change. You said you had already checked it? These governors all look alike but have to be the correct one for the rpms of engine. Do you know if this is the original transmission.? From what I know about Allisons, I would suggest changing the governor.Thanks.
Thanks for the help
thanks curtis for all the help. you got me on the wright trac and replaced govenor and cleaned screen. all is working good. drove many miles and is working great.