I had the same problem with mine in January. This has happened twice. Each time, it was a throttle position sensor cable that had broken. It missed being under warranty by a couple of days. Unfortunately, the computer needs to be reprogrammed as well. The good news is that the transmission is fairly robust, and nothing else was damaged. I did change the filters just to be safe, and topped off with Transynd.
If you can read the fault codes on the gearshift panel, and give those to the technician, he can confirm the problem. The diagnostic procedure is in the transmission owners manual.
I was coming back from south Florida and called the Florida Allison/Detroit Diesel Shop, in Panama City. They made arrangements for me to park on their lot, gated, secure, and 50 amp service. Great seafood across the street too. I highly recommend them to any RV owner. Plan on about 1/2 a day to include the computer and test drive.
95' Beaver Patriot
Beaver Ambassador Club