tow/haul problem

[Connie Darrington]

2006 Sierra 2500HD

We were towing a travel trailer; had driven 300 miles, no problem,  then all of a sudden we lose tow power, no throttle effect,  otherwise engine is still running fine.

We changed air filter and drove for another 1000 miles without a problem;  then same thing.   

At this time we had a "lift pump" installed with promises that our problem was solved.   

Drove 70 miles, did it again;  kept driving but top speed was around 45 mph.  After about 5 miles, we took it out of tow/haul mode and it started working correctly again.   

Please help!

Thanks.

 

[davester]

Any codes from the computer (either engine or transmission)?  Just because the CEL is off, doesn't mean there aren't codes being generated.

[hiking_mike]

Boost leak ?