It will do fine.
For 10 years I've had the truck and camper in my signature.
I started with a 6x12 enclosed trailer, which probable never weight more than 2500 lbs loaded. In 2012 I bought the 8.5 x 20.
I don't go 75 with it, but the combo will do that speed fine. Fuel MPG drops exponentially over 65 mph.
The 8.5x20 was over 10k loaded on the first trip I took it on. That was WAY over my truck GVWR. I decided I'd never haul my Jeep TJ like that again (in the trailer with the truck camper camper).
I still have the trailer, but only use it for camping gear and hauling my motorcycles. It's overkill for that, but it's a really nice trailer.
My 8.5 x 20 "toy box" trailerMore info on AF truck campers