So yesterday I pulled a trailer weighing approximately 6k-7k pounds that had most of my tools and some household junk in it. I decided to put the truck back to stock programming since I don't have a pyrometer installed. After flashing the ECM back to stock just for grins I checked for fault codes and have a p1488. I reflashed the ECM and still have the P1488 that won't clear. The truck runs fine and doesn't have a CEL so I'm sure it'll be an easy fix. I haven't dug into it but I suspect I'm going to find a bad MAP or CMP sensor or possibly bad wiring.

I’m assuming you have read this and performed diagnostics? Likely a sensor fault. Ha e you played with any wiring or bumped any wiring lately?

I still haven't diagnosed it, been too busy moving to Colorado. The truck is running great. I averaged 17.4 mpg running 70-75 mph with the trailer. Other than abnormally high mpg with no load or trailer I haven't noticed anything else. I suspect I'll find a bad sensor also when I diagnose.