Nothing really heavy yet I have only had the programmer for about a year. I towed about 6000 pounds and really didn't notice any problems/issues. It was not high profile trailer like a travel trailer so no wind resistance to deal with either. It was building materials and two pallets of sacks of concrete. It wasn't a long tow, about 30 miles is all, so the MPG was not something I can attest to. The throttle torque limit being gone did make it feel like it was not so much of a load as throttle response was still good and shifting was firm. I didn't feel the need to use the tow haul mode or OD off either so it may have improved it more than I thought. It was flat to mild hills until my property but that section was 3>5 mph in 4 lo due to loose dirt and a very steep hill.
I like the mileage tune much better than the OEM stock tune as it is more responsive and has a firmer shift that seems to be better suited to a truck.
PS: The dealer tried to call me on having a programmer but they could only say that I had code resets and settings like tire size and tire pressure limits that they can't or wont do because of liability or Dodge star tester programming limitations... so they reasoned that I must be using a programmer. I told them that I have the Auto Enginuity scan tool program on my PC, that lets me set all those same parameters that they can but without limitations as to range or threshold they have. Their case then fell apart and they did the warranty work as they should have done in the first place. Since they stopped all work due to tampering allegations, I won't get it back until noon tomorrow now. I also got the air bag recall done too. They said it required a re-flash for the air bag recall. So had I not put the OEM flash back in the computer there would be major problems for me to face!
If you get any flack from your dealer just tell them about Auto Enginuity and that you have a friend in Tucson that set those items for you with the Auto Enginuity scan tool. Send them to the site to verify.https://www.autoenginuity.com/products/oe-coverage-options/chrysler-dodge-family-ei04.html