I have a 2001 2500 4x4 gas truck. The check engine light comes on randomly while running on why 60-65mpg. It slowly looses power and i have to pull over and let the engine sit for 5-15 minutes and it runs fine. Then in 3 hours or 3 days it does the same thing. It's been in the shop numerous times just cannot find a fix.
Sounds a lot like the fuel pump is dying out (as most GM pumps eventually do).
But first scan and identify the diagnostic trouble code which triggered the check engine light -- and then test fuel pressure -- before buying any parts.