2006 Ford F-150 Jerking and shaking

Engine Performance problem
2006 Ford F150 V8 Two Wheel Drive Automatic

I have a 2006 Ford F-150 xlt, 5.4 engine. About 6 months after I baught the truck, it would start jerking when I would get to about 50mph. I took the truck in and they told me it was the after market exhaust that came with the truck that was causing the problem (Flowmaster). They then put a Magnaflow on instead. The problem reacurred about a year later and when I went in to the Ford dealership the Mechanic manager told me that is was my fuel injectors and that the exhaust problem they told me previously was actually a false problem. When they gave me the print out of what they did to fix my vehicl, it actually had the prior person who owned the truck, their info of the last reason why it was seen by a mechanic before they traded it in, which was the fuel injectors. Now about another year later I am having this same jerking problem. What do I do?