Engine stalls while driving?

It will sometimes start bucking and jerking on takeoff and it will act like it might stall, then it will surge and lunge forward and sometimes will kick in and start running good and other times it will continue to buck and jerk. If you turn it off and back on it will sometimes clear up but not all the time. None of this ever happens regularly, it might drive fine for hours and then the next time you drive it it runs terrible. It usually only starts acting up after about 20-30 minutes of driving and usually not until we get stuck in traffic or at a light. If you can accelerate enough to get through the rough takeoff and it can get up to a good and consistent speed it seems to clear up and will usually run fine until you stop and idle. You can always feel kind of a slight stuttering during any type of driving. It always idles stutter and slightly shaky. This all kind of started a few months ago when we had to have the harmonic balancer replaced, because it practically fell out of the truck. We ended up having to go back to have the crank shaft sensor replaced because as soon as we left the shop it started doing almost what I have explained above and after all of that was done it ran pretty good for about a month or so. Once all of the problems started we had a neighborhood mechanic try some things. He changed spark plugs and wires, nothing changed. Next we changed the fuel filter, nothing. We cleaned the mass air flow sensor but did not replace, nothing. Then we replaced the crank shaft sensor again because that's what code came up, not fixed. I forgot to mention that whenever we have the problems, the check engine light and sometimes the wrench symbol will come on. We also replaced the crank shaft sensor plug, nothing. The last thing we did was replace the throttle positioning sensor and it still isn't fixed, actually almost feels worse and is now doing it a little more consistently. It is now at a Ford dealer trying to see if they have any luck diagnosing it, but called us and said that they can't find the problem and they can't replicate what we say it's doing. We don't know where to go from here. I know it's a lot to read but I wanted to give you all the information. Any thoughts or suggestions?
The lights stay on but do not blink and if you turn it off and restart the truck, sometimes the lights will go off. Bucking and jerking
The only code that ever comes up is po320. Also we did unplug the battery to try and reset the computer.