Jake, I put a banks econotuner on my 05 duramax along with a different exahust, it worked great for a month then coasting down a long long hill coming down the alcan all of a sudden my engine light did that and truck wouldn't rev up just limped down the road til I could pull off. Was in the middle of nowhere so shut it down check elec connections, fuel etc couldn't find anything. Started it back up and all was fine and never did it again, check eng lite went off and everything. So by the time I got to Or. bought a tractor built a flatbed out of a boat trailer did the holidays I plumb forgot about it. Til...Had the trailer loaded for home @10 ton, was pulling out the driveway and the same thing happened. Backed back in checked everything, turned it off and restarted and same thing as soon as I pulled out. Backed in, called Banks they said that the extra power from the system plus the new heavy load I was pulling was making the slip sensor on the transmission set off the "limp home mode". They said to just go a couple of miles down the road limping, turn it off, then start it again and it would reset to the new parameters. I did, it did, and made it up the Alcan with the load just fine after that. Haven't had a problem since and when I talked later to a gm mechanic, he said that it happens sometimes even without the extra power of the banks. Sorry for being so long winded, but yours sounds like what was going on with mine. Good Luck
Rick