Intermittent downshift and loss of power 06

[jdevault]

I have a new 06 GMC 3500 with 450 mi on odo. Three times now, it has downshifted and suffered a huge loss of power while crusing at about 55mph. Turning the key off and restarting clears the immediate problem. No codes are set and no messages on DIC. My mechanic is pulling his hair over this one !

[More Power]

Wow..... No codes....

Generally any problem that puts the engine/drivetrain into "limp" also illuminates the MIL lamp, and stores a code.

If possible, leave it in "limp" long enough to read the codes.

Jim