I have a 2004 f150 fx4. My truck starts to jerk around 50-55 mph at 1100 rpms and again at 80 mph. Please help.

 

When was the last time you had your spark plugs changed? Any check engine light?

Mine did that too at 45 MPH, when it locked into OD. It was a misfire. Plugs were shot. Had them replaced and it has been running perfect for over 20k miles

 

Your spark plugs are dying. Get them changed now. Until then, don't let the engine be under load at low RPM. Kick the pedal down and force a downshift. If you let the truck start jerking, you're going to cause other issues.

 

Did you get your plugs changed? Did it help the issue?