We have just recently towed a 5x8 cargo trailer from Colorado Springs to Fairplay. This trailer is a bit heavier than a standard 5x8, it's not aluminum, it's made of steel. (WW Trailer) It has electric trailer brakes so I have added a Prodigy brake controller. The tow from 6800 ft to 10000 feet was much better than I had expected. I was anticipating a sluggish trip. To my surprise, the trip was not bad. Yes, I knew it was behind me, but it was not objectionable.
Our other trailer to tow is a 27' travel trailer. Not going to tow that with the H3. That duty is dedicated to the Tahoe.