Take your truck and trailer to a certified scale and get the real weights of the total rig - individual weights of each truck axle; then reweigh just the trailer on the sales and the truck off the scales - still hooked up. Try to get the two trailer axles on different scale segments. Finally drop the trailer and weigh just the truck alone.
That will give you the exact tongue weight, along with showing you how much the trailer lifts weight off the front wheels. If the trailer axles show different weights - it will indicate which end of the trailer is heavier.
I had an F-150, and I soon realized a 28 foot trailer has more sail area than the truck can handle in certain wind / travel conditions. You might need more weight in the truck to steady the rig.
The other suggestions are good fixes, but you need to know the real weights.
Also, with that light of a truck and heavy of a trailer - you might need to keep your speeds closer to 55 mph.