Hi josh,
well first off according to the serial number you posted this is not a H100XM, it is actually a H100FT.
Ok now we got that straight...
The guys from the service center you had come out and look at it did go down the right track. Replacing the sensor was one of the steps. But since this doesnt seem to fix the problem i have a question.
Is this a mazda engine? or a GM engine in this truck?
If a GM engine then yes the flow chart does say to test the FAP sensor and circuit and ultimately replace the sensor if the wiring checks out ok.
But if this truck has a mazda engine then it refers to the hydraulic pressure with the mazda engine and also refers to the engine oil pressure with the 2011 GM oil pressure sensors.

So clarifying this bit of information may shed a different light on the diagnosis.
I found it curious that in the troubleshooting manual they referenced ALL the sensor circuit diagrams, maybe that's just being overly thorough by hyster engineers... i just cant say.

All in all they did start down the right track by checking the FAP sensor and replacing it though. I just think since it did not fix the problem it could possibly be a different sensor or ultimately the VSM or ECU software or something. I'm sure they checked all this when they were running diagnostics on the truck.
I have a question though...
did they send out the same tech on each of your service calls?
reason i ask is maybe you should request a different tech to come out and take a look? a different tech may have a better perspective on the problem.
One other thing also... is this truck still under warranty?
If so let them handle it... between the dealer and the factory they will get a handle on the problem and fix it... eventually...
sometimes these problems can be tricky and it takes time to work it out, especially if it is a factory issue. Just stay on top of it and don't let alot of time pass before calling them.

good luck