Today while coming back from the Black Hills, pulling a hill at 65 MPH with my toy hauler behind, truck downshifted and kind of jerked. Trany would not upshift back into 5th gear and check engine light was on.

Pulled over and shut truck down. Restarted and everything was fine other than light was still on. About 20 miles down the road, the same thing happened when a downshift was forced. I pulled over and checked DTC, I got a P0700. I continued on for another 50 miles without any issues other than the check engine light on.

I decided to pull over and put my factory tune back in. Truck ran flawless the rest of the way home with no more check engine light.

Truck is a 2005 running a predator 40 HP tune.

Anyone have any ideas?

Need to have the codes read with a reader that will read the TCM. Local Autoparts stores may be able to help. P0700 just means that the TCM requested the CEL to turn on. There will be more codes on the TCM.

Moved to Allison OEM.

if it put you in fourth and you were driving normally (steady state) before hand I bet you have a P0735 - slipped in 5th.

sounds like classic limp to me.

ya limped it start saving for trans upgrades

So... i have the same issue, oh well. how many times can an allison limp before it's fried? today the tranny temp got to 240~ish with a total weight of 22300 lbs (pickup, trailer, and calves)

OK had the codes read today. I get code P0735. I assume this means either new tranny or new truck.

OK had the codes read today. I get code P0735. I assume this means either new tranny or new truck.

Or cut the power to stock.