GMC tranny issues
 

hey so my boss's truck is a 2006 GMC 1 ton and when hauling a small load such as a 6 wheeler and about 500 gallons of water it will kick out of overdrive going up hills. It will then stay in 5th gear and will not shift down or up. He then has to stop and put it in park then shut it off. The tranny will not even shift into reverse. All he has done to it is the exhaust and the small diablo programmer which he keeps on the economy and towing option. He is able to turn the overdrive off manually when approaching a hill. This will happen on and off whenever it is most inconvenient. Any help would be great. thanks in advance.

mike

oh and i already told him to buy a dodge, he wont budge though, he's an old gm fan for some reason

Did he check for codes yet?

Shouldn't it still be under warranty, let the dealer figure it out.

it just came off warranty he said, its gone through alot of miles. It almost sounds like it doesnt have enough pressure to hold the TC locked up

my dads did the same, in the end it was the fuel filter ( i know how this sounds).
my brother in law works for chevy and when i asked he said the ecm would try to compensate for the lack of fuel-even if it meant the trans had to slip/not perform correctly( as dictated by the ecm)

well we just changed the fuel filter about a month ago. this has being doing it for the past year from what it sounds like