I think you are just not used to hearing an engine having to rev at high rpms to get up the grades.. It's usually 'normal' for an engine to do that when it's working hard...
Towing a TT is not like going to the grocery store, so it'll need to work.
You are at the max tow ratings of that truck, so it's gonna have to work to tow it.
Get a little bigger truck, with the same TT and it might not have to work as hard..
Take my setup for example... I've got an F150 that is rated to tow an #11000 TT...
The trailer I tow with it weighs a tad over #5000....
Guess how my towing experience is?? :) :)
Been towing trailers for over 35 years and have towed overloaded from coast to coast back in the day... Long before any of this "tow rating" stuff came into play...
So, you just have to find your own towing comfort level and go from there to match the trailer to the tow vehicle...
It's not always about the vehicles "tow rating", because it ain't the same as going to the store.... ;)
Good luck!
Mitch