V-Cross trailers seem to have heavy tongue weights. Looking at similar trailers on the Forest River site, you probably have a DRY tongue weight of 700 to 800 pounds; more with LP tanks, batteries, options, and loaded. You may very well be at or over the payload capacity of your truck.
You don't mention what version of F150 you have or its payload capacity. (It's on the door/door frame) Some optioned high-level F150s have payloads as low as 1,100 pounds. Check out your payload capacity.
Also, don't forget about (in addition to your tongue weight), the weight of your family/pets, tools, hitch, coolers, generator, etc that you load in the bed of your truck.
If you add all of this up and include the tongue weight of your trailer, you may very well have an issue.
This is also quite a long trailer. That also may be contributing to the loose feeling you are getting.
Putting less pressure on the bars is probably the wrong direction to go. You need to transfer weight off of the rear of your truck and onto the front of the truck and the trailer axles. You do this by putting more pressure on the bars.
2012 F150 FX4 Ecoboost, 2016 Surveyor 274BHS
2003 Yamaha FJR1300, Demco Premiere Slider
1969 John Deere 1020, 1940 Ford 9N, 1948 Ford 8N
Jonsered 535, Can of WD-40, Duct Tape
Red Green coffee mugs