Two months ago the speedometer in my 1992 f150 started fluctuating, and then flatlined. Truck started shifting hard at same time. I took the advice I found in the forums and switched out the speed sensor on the rear axle and bought a used PSOM online. The PSOM was fried, so I ordered another. Odometer and speedometer worked with 2nd replacement and shifting was smooth again - but the speedometer still fluctuated 20 MPH up and down when going over 45. Time to get a pro to help. Took my baby to top electrical mechanic in Orlando. Mechanic flushed and serviced rear axle, checked tone ring and said it was in good shape. He ran diagnostics, traced each line from cluster to axle, and said the PSOM was faulty. OK... seems a bit odd, but I ordered another. Another week goes by and mechanic says the third replacement PSOM is bad. I am assured that the diagnostics are accurate and there could be no other problem. He says I might have to buy several more to get a good unit. Seriously? I have now ordered three more PSOM units - to make sure! Any suggestions out there?