Got a friend with the 5.4l in a '08 F150. He tows a 5k lb trailer and he experiences shaking of the motor, almost like it is misfiring. He shuts it off, and then restarts it. All is well. However, this only happens when he is towing at a slow speed. Around 30 mph, in 2wd, with the trailer.

He brought it to the dealer twice and they told him his truck is fine. Which I'm sure is a line of BS.

I'm thinking it is the electronic throttle body...

 

I'd be more incline to think it's in the tranny. He either is having a cavitation of the fluid in the tranny which can make one shutter or the torque converter is weak. Might wanna try a tranny fluid swap and see if that helps. Does he by chance have an auxiliary tranny fluid cooler? If not, he probably could use one towing 5000 lbs.

 

if only he had a manual..

 

He's got a XLT 4x4 with the Ford towing package. I'm pretty sure it's got one. If not I can find out.

What the strange part is, that he can park it, and the engine is still shuddering. Which almost makes me want to believe it is the throttlebody on it's way out or there is something else going on.

I don't think it's the tranny, but hey, you never know.