hoping someone can tell me what is causing my 2009 2500HD sikverodo 4x4 tranny to slip when it shifts from 3rd to 4th. This does not happen each time, only when cold or after warming up in the morning. Only once or twice then no more. Have had the vaule body cleaned and they found foren material in it. this work for about two weaks then started again. took back and tac said pump rings and seal needs replaced. worked good for four days then here we go again. there are NOT CODES. Anybody have the answer to this????