Check engine light comes on towing a trailer with 2007 Chevy 2500 HD

there are a number of reasons for this light to illuminate~ is going to be with the emissions mostly~ the evap system must breathe easily...with that added load is constricting proper combustion~....just a theory,

If the light came on then it stored a code, what is that code?

All that added load probably stressed the drivetrain to the point that the engine is overheating or the oil level is low. Check the vehicle. And actually look at that red light that says HOT.

try putting fuel injector cleaner in it ,could be as simple as that , note if you get stabletrac , reduced power service light it will use usually make that code go away within 10 minutes