Ford Repair: throttle hesitation/vibration, ford f 150, vacuum leak

Question
1999 Ford F-150 2wd 4.2LV6 Auto w/OD
When traveling at approximately 40mph with slight throttle applied I get a vibration. If I accelerate or decelarate htis condition will go away. The same condition occurs with the transmision in park and applying throttle. Runs smooth until 1600rpm and then it feels like I start loosing ignition or fuel. If I run up the rpm's a little higher it smooths out again.
Check engine light was on. Had a O2 sensor bank1 sensor 1 (lean) code along with a Manufacturer Control fuel metering code. I had another guy do an OBd diagnosis. He said that ignition system was not breaking down, MAF & MAP sensor looked ok, worked the transmission through the gears and he said it appeared to operating ok. Not sure if lock up torque converter is working properly as we did not drive the truck while testing it. He also said that the injectors were all working but was not sure if one or more may be weak as his machine takes an average of all 6 injectors. He also siad the oxygen sensor continues to read lean on bank 1 side.  
I have tried changing plugs, wires, and fuel filter none have corrected problem. Would the oxygen sensor cause this condition? I have been told to check fuel pressure and test fuel injectors individually with a noid light to see if anything reveals itself. Any other ideas?  

Answer
Hello and thanks for the question...I'll try to help.
It isn't likely that an O2 sensor would cause a engine shudder. What I would suggest is that you look for a vacuum leak and also take a close look at the ignition system. It is more likely to have a breakdown in that system.
Erik