2008 GMC Sierra 2500HD - limp mode mystery

I have a 2008 GMC Sierra diesel and towing a 25 ft Airstream in a headwind. At 65 mph we’d go into limp mode but at 80 mph we were fine. We had one historical code for fuel pressure, but went into limp mode 4 times. What was the cause? We suspect a fuel pump issue. What do you think?

My first idea is cooling system overheating. Could be fuel pump tho.

If you would have the error codes read and posted here, we might have some reasonable ideas.

As it is, all I can say in this information vacuum is; You have a problem.


Anyone besides me wondering why they would go 80 mph with a travel trailer being towed by a vehicle that has problems ?


In my area, pulling a trailer while going 80mph is inviting a ticket from the highway patrol


gonna have to provide more info about “Limp Mode.” Do you get any other error messages? Anything about cleaning engine or DEF? (I’m not actually sure if your diesel has anything DEF related on it.)
does the truck actually go into any kind of derate mode? Or does the dash just say it is. If it does go into a limp mode that affects drivability, how do you get it to 80mph?

Could a transmission overheat cause limp mode? This is just a wilde guess. Maybe going faster makes it down shift so it stops overheating.

Those in the east coast believe everyone should maintain the same speed of travel or the speed of the fastest driver in the interest of safety.