Ford Truck Enthusiasts Forums - SES light while towing

I just got back from a 2600 mile trip towing my horse trailer. It was empty (2300 lbs) for the first half and loaded with about 2000 lbs on the return. While going uphill in cruise at about 70mph, I got a SES light on 2 occasions w/ trailer empty, and 2 occasions w/ trailer full. I read the codes after each half of the trip and only found the 1211 code. On all occasions, the SES light cleared after a couple of minutes once I was over the peak of the hill.

I could also hear a differnt sound in the engine - it sounded like the injectors were not firing evenly. The truck was at about 1900 rpm and I am running a 40HP Tow Tune on my Diablo Predator.

I have thousands of miles towing using this tune, and I have never seen the SES light come on during previous trips. The only mod I have done since previous trips is the 6637 intake.

I've done some searching and reading, and learned that the HPOP may be the source of the problem. Is there any easy way to determine if the HPOP is the problem? Is this something I should be concerned about or let it go?

I am planning to get a larger exhaust and set of gauges, then add the DP tuner in the next year. These will all support a much larger horse trailer we plan to buy next spring (~10k lbs empty plus 5-6k horses and gear).