What octane fuel are you using?You should be using 93 if it's available where you live!!!

 

 

Were you previously able to tow the trailer without overheating? How was your trans temp looking? What gear was the trans in and what is your axle ratio? Is your trailer really only 7K #? Seems light for a 32'.

Personally, I would start with returning to a stock tune and see if that helps. If not, then I would start looking at the cooling system.

 

Rad is clean of debris? Being a 12 have you flushed the coolant yet? Obvious using T/H...

 

Yeah, that's what I was thinking.
You sure the 7.000lbs isn't the dry weight? Your trailer might be much heavier than you think.

Still, a 6% grade for 3 miles isn't all that severe, certainly not what I would have thought to cause your engine to overheat by that much.
Was there a strong head wind?
Are you using Tow/Haul mode? What rear end differential ratio is your truck equipped with?

As others have suggested, start by disabling the tune and see if that helps.

 

couple things. First, what gear were you in and what speed? 6% is a decent grade, especially towing 8000+lbs. higher rpm is not bad for the motor and allows coolant to flow thru the radiator better as well as fan work more. Lower rpm and high boost generates a LOT of heat.

 

Assuming all your supporting equipment is in order, a lower gear and stock boost should be your first attempt to fix it. Both should reduce exhaust temps which will reduce the heat the turbos dump into the cooling system. The higher water pump speed also helps cool the engine.

 

5 percent grade with over 4k Lbs, I forced it into 5th gear kept the turbo lower as you can see mine(stock) is 1/4 of boost. Higher RPM helps.

This video I allowed the ECU to do everything moments before - lower rpm higher boost so im sure the long haul up a grade will cause a lot more problems. Same grade before I locked out gears.
http://photos.app.goo.gl/sfhE7BtTX7ghgvSh7

 

This has become "normal" for a lot of people. Some people never towed and just "discovered" their truck does this. Others claim they never had a problem, now all of a sudden the truck gets hot. It's an ongoing issue for many who tow about what you're towing. People have tried all sorts of remedies, a full-race radiator upgrade, Intercooler upgrade, larger transmission cooler, an aftermarket oil cooler, etc. Some claim it has helped, some still report issues. The only thing that seems to get people up over the hill is DOWNSHIFTING and SLOWING DOWN. What you want to do is keep the RPMs up. I pull miles in like 3rd gear at about 3K with the same weight as you. When you do this, you will be "out of boost" and the turbos will stop pumping hot air into the motor. Also the water pump is circulating the coolant more. Aside from that, all you can do is double check your fans are working properly.

I have yet to see anyone who has fixed this issue. I think that's just how it is. The turbos get hot, dump a ton of heat INTO the motor and BAM, you are overheating.

Regarding your question, the reducing power and CEL are built into the programming to cool the motor down. The PCM will start shutting off cylinders, dump more fuel, etc. to cool the block. You won't be hurting anything if it reaches this point. The problem you'll have, is that in the reduced power mode, towing will be impossible with the weight you're towing. So it's best to either avoid it, or pull over and let it cool down before proceeding.

Another strategy I have used is leave early so when you hit the big grades, the ambient temps are lower. This helps the engine not heat up so fast.