Towing my 6000lb trailer with my 2017 XLT 3.5 Eco, 3.55, Crew Cab 5.5 bed - I am impressed and satisfied with the performance. Of course, an HD truck will tow better, yes. But, I like the everyday comforts of the F150 much better than the prior Duramax.
I think you have two issues: 1)something not right with the truck, AND 2)too much trailer (length and weight). If you can figure out #1, you can deal with #2.
I understand all the ratings; I'm just speaking from actual experience. I wouldn't enjoy towing anything heavier than 6k, and longer than 25' with a 1/2 ton truck. I like to be in control of the trailer, not vice-versa - and this can best happen with a truck that weighs equal to, or more than the trailer you're pulling. I know some will disagree; just my experience.
Wish you the best of luck.