possible transmission issues
 

I've got a 98 f150, the 4.6 variety. I was pulling a trailer(unloaded) and while speeding up, under 2krpm, my truck started shuddering, like the feeling of a waterboarded dirtroad. I backed off the gas and then resumed acceleration and it was fine a while. Well during the rest of my trip it continued to do it intermittently, backing off the gas would help find the gear I guess. It threw a code, but the code was for missfire cy1, which has not popped back up since its been cleared.(today). Any ideas? This a bad deal where I'll need a new trans, or might the of be done. Oh yea, taking the truck out of OD seemed to help....ie. Not doing it as much or as bad.

Torque Converter
 

Have a transmission service garage check it out. Could be the torque converter.

if you are still in shudder condition, find correct misfire and replace that coil and boot. same thing happened to me and i also thought it was transmission related. first time all i had to do was replace boot. more recently coil and boot. need to do as soon as possible for it does put undo strain on OD.

Yes to above, check those things. An engine misfire will show up worse under load, where when not under a load will not be as noticeable. It could also be a brunelled cross joint in the drive shaft. If water got into a drive shaft cross joint bearing and rusted the needles that can make a shuddering sensation. A light load will not be so bad, a heavier load will make a shuddering depending on how bad the needle bearings are in the U joint. So do not over look that possibility.
good luck
Darryl...