Smoke from Tow Vehicle

I'm asking for your thoughts. My Tow Vehicle is a 2015 Chevy Silverado 2500HD Gasser with 10,000 miles that I bought new in the fall of 2014. This is the third season towing with it. We went on our first camping trip Memorial Day weekend and we had just left our home. We had driven only 6 miles when I smelled burning rubber while going up a 1/4 mile grade. The grade was probably around 20%-25%. I pulled over and a blueish smoke was billowing out between the cab and box of the truck as well as the the underside. So much so that I called for the Fire Department. Fortunately, there was no fire and the smoke subsided within about 5 minutes. I had no further problems the rest of my trip to the campground or on the way back home. The only things I can come up with as possible causes are...I used the parking brake while hitching up and when I released it, maybe it didn't release fully but there was no smoke coming from the wheels when I stopped. I re-applied the parking brake while on the side of the road and instead of releasing it slowly, I let it spring back (it's the foot pedal type where you push on it to release it) in case that was the cause. The other possibility is, I had the truck treated with Krown rust prevention (A sprayed oil type of rust preventative) but that was 9 month's ago and it hasn't dripped or smoked from that treatment since last fall and this was the third time having the treatment without any issues. I had it in to the dealership where I bought the truck when we returned home and they couldn't find anything wrong. No signs of burnt or scorched areas under the truck. I'm at a loss and a little worried about future towing with it. What are your thoughts?