Engine overheating - spewing coolant
So I'm on mission headed to Strange Creek & Webster Springs West Virginia today. I'm towing my 22' enclosed trailer - loaded but not nearly as heavy as in the past. All things fine until I hit the first steep grade up Rte 68 (maybe it was Rte 70 still - not sure) towards the Cumberland pass - top of the mountain (Western Maryland headed towards Morgantown) - its a steep grade - nearly all the way to the top and my engine EGT spike,, my Check Engine light starts flashing, power drops off, all sort of noises start being made by my engine, and I can smell coolant burning. Thankfully I'm literally in the exit land for the rest stop so I come to a very abrupt stop, shut off my engine, pop the hood and see a ton of coolant all over the drivers side of the engine bay. its a new resivouir cap too. So I know the cap seal is good. All came from the resivouir. It spewed all over the place.
I dumped in 1/2 gallon of spare coolant I had, started the engine - all things seem fine - head on back down the road. 10 minutes later - next mountain and it overheats 3/4's to the top. EGT's on the factory idiot guage spike to red, check engine light starts blinking, coolant burning smell - pull over and same thing - less then 1/4" collant left in the resivouir tank. Pour in more coolant - start engine - all seems fine.
over and over - same scenario until finally things leveled out south of Morgantown.
Truck is running great - other then the coolant / overheating issue - truck returned 15.3mpg hand calc'd - filled up in Dunkirk MD and filled up in Flatwood WVA before heading to my final destination.
Trans is fine, air filter light wont go off even though I put in a new air filter, mileage is good, not hot out - I dont get it. What is wrong? Thermostat maybe? Check engine light goes back off once I let off the go-pedal and the RPM's drop - then the engine starts cooling itself and EGT's start to drop off.