I have a 2008 F150 5.4L crew cab I purchased brand new. At 70K miles the truck began to shake after towing my 6x12 enclosed trailer from NY to NC. It didn't do it again until a month later on a trip to Georgia from NC when I pulled the same empty trailer. The shaking stopped each time when I shut the truck off and restarted it. I took it in and had the transmission overhauled since they said it was damaged from towing even though I always used my overdrive while towing. Last fall the same exact thing happened while pulling my landscape trailer with a riding lawn mower a distance of 300+/-. I shut the truck off and restarted it and it stopped. I took it to a local dealership and they said the transmission was shot and I had it replaced. Last week the same exact thing happened again! The check engine light never comes on when this happens and always stops when I shut the truck off and restart it. They now say it sounds like an oil thinning issue only after towing due to high heat. Sounds like no one knows what they are talking about! Anyone else have the same problem?

 

The definition of insanity is "doing the same thing over and over again and expecting a different result." So you've done some long distance towing, and every time you do it, the truck shakes, but stops doing it after a shut down and re-start. Then various shops diagnose the problem as the transmission needing a rebuild. That's not a cheap date!

The first question I'd have is whether or not your truck has the Towing Package with the Transmission Cooler. If it doesn't, that may be the root cause of your problems. Without a cooler, the transmission fluid can get too hot and heat is the Kryptonite of automatic transmissions.

You also said you always tow in overdrive. That's not always the best idea. When you tow that way, the transmission tends to jump in and out of overdrive. Doing that tends to heat up the transmission fluid. See where that one is going? It's best to tow in Tow / Haul mode.

Finally, you noted that you're not really towing huge / heavy trailers. That's usually a good thing. But depending on a number of factors like aerodynamic drag, tire inflation pressures, etc, even a small trailer can cause pretty significant drag on the tow vehicle - which causes additional strain on the transmission.

The first thing I'd do is taste / smell the transmission fluid. If it's getting cooked, it will look brown and smell burned. (Good ATF is generally red in color and somewhat sweet tasting.) If it's burned up, chances are so is your transmission. If that's the case, I'd be looking into the Transmission Cooler thing pretty quick.

 

Go through the normal checklist... coils, fuel driver module, phasers, etc.. I would change the oil to 5w30 or 5w40 and see if it happens with a thicker oil. If thats the case phasers need to to be replaced. Worth a shot. Same thing happened to me, although without towing. I replaced coils and fuel pump module and it was fixed. I plan to do my phasers and a mellings oil pump when the weather warms up, because I have timing problems when my engine is hot and the weather is hot. Good luck