So I bought a 1996 Ford F150 XL (4.9L Straight 6 RWD Automatic Transmission) anticipating to put some work into it...

Well since I bought it I've put close to $700 into it.

I've done the following:
New Crankshaft Sensor (went bad)
New Front Upper and Lower Ball Joints (Left and Right)
New Front Brake Pads
Had welding done to the exhaust
Changed the Oil
Flushed the Radiator and put new Antifreeze in (the **** that was in there was solid brown and you couldn't see anything)

Well needless to say I cleared up the piston misfires (caused by the bad Crankshaft Sensor) but I can't seem to fix the "System too Lean (Bank 1)" and "System too Lean (Bank 2)" codes... The crankshaft sensor wasn't plugged in I realized so I plugged it in, cleared the codes and drove it up and down the street quick. They weren't there but I'm not sure I drove it enough so I'm going to drive it some more tomorrow then check. But assuming they're back what suggestions do y'all have?