Update: Truck still shakes bad after the shim kit install. Dealer blaming my brand new trailer, so I'm going to hook to another one this weekend. We'll see...

 

Good luck, but I went through 4 trailers, plus the one that Ford used (thier own) when they test drove it. They all equally exhibited the same thing, but they still contributed it to the trailer! It's not the trailer. Take that same trailer and pull it with another vehicle (other than an F150). It'll tow fine. Trust me, my wife's Pathfinder, 3.3 V-6 pulls it up to 85 mph with NO problems.

 

I loaded my JEEP on the trailer. This vibration is gone with a load on it. The shim kit fixed that. I can live with a vib when empty.

 

You're luckier than I then. When I loaded the trailer out it increased the vibration in my case.

 

My husband has a 08Ford Sport Trac we've had it almost a year and now when we pull a trailer (simple little flat bed) or our boat (a 16ft sunglass with a 40 hp) the truck seems to start acting up as if it stops pulling I do not know if it's the transmission or what cause if we cut it off for about 20 mins then it'll do fine. HELP Please?!?! I love our truck