Our TV did not have an issue in the mountains as far as pulling, and maintaining a 60-mph speed, however the ride was horrible. Every time we hit a bump in the road, it seemed like the whole TV shook or bounced (it is the best I can describe it).
I use the wifes '16 1500 4wd crew cab short bed 142" wb truck when in and out of muddy worksites pulling a bumper pull 10k car hauler with around 8200-8300 lbs on the trailers axles and 980-1020 lb hitch weight on the truck. I notice much the same when coming on and exiting many bridges at highway speeds. Suspension is simply to soft.
I also use my 2500 Dodge/Cummins 2wd short bed 142" wb pulling the same load on the trailer. There is no bucking and a very smooth ride.
You won't regret upgrading to a 2500 truck for towing 8k-10k trailers.