Check the chassis batteries for good contact first. I just went through this. I pulled the control unit and sent it in for testing, nothing wrong. Took the coach to an Allison repair facility and they found really loose connections. This was weird as I had recently tightened them up. On coaches with the ISC engine, there can be an issue between the cruise, the transmission and the Pac-brake. Since mine is a "mechanical" engine like yours, there is no way the Pac-brake could be involved.
An additional thing to check for is when you start the engine and the throttle is non-responsive do you have a * type thing showing in the transmission selector display? This could be an indication that the transmission is not receiving a signal.
I am without my paperwork now but expect to have it by next Monday. Check these things and let us know. Also, the coach originally came with information on the Cruise Control with diagnostic procedures, if you do not have that, it should be available on the ACA Tech website.
'99 Alpine Coach