Today we hooked the truck up to a scan tool. Not sure what exactly it was called (just know it costs about $5000.00)but it measured air-fuel ratio as well as many other things including NO2. Based on those readings (one number was up around 1300)we decided to disconnect the O2 sensor and the truck ran great while at idle. That number (wish I could remember what it was) dropped to between 350-450. So we thought we had the problem solved....buy another O2 sensor....wrong. Test drive brought it right back to where it was.

Next step, run the fuel pressure regulator with injector cleaner. Once again, the truck ran a bit better for a mile or two and then the symptoms returned.

I then tested the fuel pressure regulator by disconnecting the return line to the tank after the regulator. I started the engine with the pressure guage on to see what would happen if the fuel was routed through the regulator into a bottle instead of to the tank. The pressure went up to 48 pounds with the line routed to the bottle but dropped back down to 40 with the line routed to the tank.

Fuel pressure regulator??? Other suggestions???

Help....please....