I had this code keep coming up. Before I got a code for it , The 4.3 was running rough so we replaced plug wires and plugs,. Then I borrowed a OBII to see what the check engine light was meaning. It came up PO122. Said low voltage. I got that all checked it was ok. I even changed the Throttle Positioning Sensor. Still ran like before. I checked all the wires for rub thin coating and everything,Still the PO122 code came up. Went online searching again. Checked the fuel pressure. Went up to 65 and feel to 40 in less than a minute. The persons website " might even been here not sure". Said it could be the Fuel Pressure Regulator. So he said once you remove the airbox top if there was a clean spot you would know the gas was leaking from the regulator . I opened mine up and there it was the clean spot. So I bought and installed the Fuel Pressure Regulator and started it up , Runs like a new one and the the PO122 code has not came back. Just amazing how that code was so misleading and was something else. Hope this helps some one. When the problem started it had a real strong smell of gas and idled real rough and even worse in gear and would die.

 

Thanks for sharing.

Also This site has a number of discussions listing odd things around this code.
obd-codes.com/p0122