CPS Code Problem

I had my 1996 Buick Regal 3.1 rebuilt. Seem like rebuild was a good job but when I picked it up and got about 5 miles the "Service Engine Soon" light came on. Took it to AutoZone and a PO336 code was on. They cleared it but 5 miles later it came back on. Took the car back and shop replaced sensor. 5 miles later light came back on. Had the light cleared again, 5 miles later light came back on! Took it back to shop and they changed the sensor again but guess what? Light came back on. They said drive the car for a couple of months and see if the computer may clear the code. The shop check everything so they said. Any ideas? Anyone had this happen before? I am out of ideas.