As far as trailers go, yes. I have towed: 11000lb cargo, 10000lb bobcat, 1500lb motorcycle. I'm not here to ask if someone can tell me how to air up my truck tires, or act like they know what my truck is capible of.
A good tight tarp and slowing down is your only hope for any better mileage with that truck and pulling a 4000 lb anchor behind it. If your pulling the above loads with that truck at 70 to 80 MPH , please stay in Nebraska and off of I 80, thats border line insane,
Good Luck