PSOM is programable speed output module. It allows you to compensate tire size, but it's also a nexus for all things speed related.

It holds your odometer setting which are not easily changed or transferred. You can't get a new one , but it can be repaired.

As with most things, I get junkyard replacements, test in place & use for diagnostics.

 

Not sure the question, first thing I'd do is verify the MLPS is adjusted first, not hard to do, but I don't have the actual steps or illustration.

 

I think they were asking if the limp mode has a fix. Like Scndsin said, the transmissions on these trucks rely on the VSS (Vehicle Speed Sensor) for the proper operation of the transmission. I had a severed wire on my VSS causing hard shifting. Once repaired, it went away. However, while diagnosing that, I learned that the VSS signal goes through the PSOM on the back of the speedometer before getting to the PCM. So a failing PSOM can induce "noise" in the signal the VSS is giving, causing hard shifts.

Does your speedometer work, and if it does is it smooth or does it jump around?

You can test your VSS and it's associated wiring. There's a 2 pin test plug under the hood on the drivers side near the hinge. Raise the back wheels off the ground with jack stands, put a volt meter on the the two pins, and have someone slowing bring the speed of the vehicle up to 35 MPH. You should see the voltage at the test port smoothly increase from 0v to around 3.5v as they accelerate. Make sure to be careful and chock the front wheels so the vehicle can't move. Do not stand in front of or lean over the vehicle while your helper is accelerating.

With the broken wire on mine, I was seeing a constant 4.8v on that test port. Once repaired, I saw the proper voltages.

Good luck!