Sounds like too much $$$$$$$$ to me.
I took an ATEC ECU from a bus with an HT748 trans and installed it in a bus with a V731 trans. Both vehicles were ATEC controlled transmissions. I swapped the PROM from the original V731 bus into the ECU from the 748 - donor bus. Worked fine.Both ECU's were the "Sealed Standard/Sealed Plus II type.
The PROM is located under the small cover with 4 small bolts, on the back of the ECU.
The PROM has all trans shift and control info on it.
It has a label to tell if it has been tampered with, I didn't care. Might be worth a try.
If you want to try it, call NIMCO again and ask for an ATEC ECU from a bus that has the same style of ECU that you have.Tons of transit buses had them. Try a local transit garage too.
WTEC does NOT have a servicable PROM, gotta go to the Allison dealer to have the program burned to it.
New WTEC ECU's do not come programmed - WTEC2 or WTEC3.
Hope this might help you. Best of luck with your repair.