help with 2500hd transmission
 

hi guys new to the forums. but my step dad is having problems with his 2002 sliverado 2500 8.1 allison 1000



he says it drives but at random times the rpms jump to 4500 and go to 2200 and stay in 4th gear. and stays at a low speed



when he turns it off and opens the door and stats it again its back to normal unitll it acts up again.



we replaced the nsbu and it still acted up.



then we fill it wil new oil when its been running for 3 mins and the level is half way in the hot area. is that normal?



ive looked everywere for a fix for this and noluck.



he reanly pulled a travel trailer from Houston to angleton. He told me it ran great going over the ship channel bridge. when he came hold it messed up like on line 2 of the post



please help. no ignore he relies on this truck to pull a travel trailer from angleton to Houston. in a couple weeks