i got a 2001 2500, with a rebuilt tranny and shift kit... problem im having is when the engine is cold it shifts how i want it to, going through all the gears properly... when the engine gets hot it shifts 1st 2nd fine then 3rd 4th o/d is super fast, doesnt even seen to use 3rd, im only goin bout 65km and im done all the gears... then when it gears down up a hill it shifts down 2 then back up 1... i dont get it...is it related to the o2 sensor???? im not a mechanic, so any help would be nice

 

Who rebuilt the tranny, and when? I would be going to see them, and see what they have to say for themselves.