Ford F150 Forum - Community of Ford Truck Fans

Ok guys, I'm at a loss on this one. Been trying to diagnose this problem for a while now, but nothing is working. I have a 2001 F150 with the 4.6 V8. The problem started when I was pulling a travel trailer down the interstate and the truck began vibrating real bad and lost a good bit of power. Initially I thought it was a ignition coil, as I've had a similar thing happen in the past on a different F150. Made it to Advance Auto and they said that Cylinder 3 was misfiring. Changed the ignition coils and all spark plugs, but didn't fix it. Had a mechanic look at it and he tells me that cylinder three had a hole in the center of it. The spark plug I had changed from this cylinder was actually missing half of the L-shaped piece at the end of the plug, so this was very plausible. So I tear the engine down only to find out the cylinders were in great shape. Not a happy camper at this point, but at least I got to replace the head gaskets and all other gaskets. Got the engine back together and have since changed the O2 sensors, MAF sensor, DPFE sensor, all new fuel injectors and still same problem. The only code now showing is P0172, but both banks are showing in the negative on fuel trims. I really don't want to keep throwing parts at this thing when I know the fix is most likely something simple. The truck can take a second to start and sometimes you have to give it gas to get it running, otherwise it kind of sits there sputtering and not wanting to idle. There is definitely a small backfire from the passenger side exhaust (it has dual exhaust), but no black or white smoke. However, you can smell that it is running rich. When driving it, it vibrates the most once you've got up to speed and just cruising. I've also checked the vacuum lines and they're all good. I'm just wondering what else I can check, or if anyone has had a similar problem.