Okay, the shop clarification is that it is the ECU only, not the MPEM.
No usable fault codes. They confirmed the issue through throwing parts in and swapping out at a labor cost of $300. ..jeez.
I'm going to pull the boat back and take a shot at a DIY fix in the garage w/ take-off parts. As I understand it, the ECU is plug-n'-play so I would not need to mess w/ any DESS re-programming to the MPEM if I picked up a used ECU. Need a reality check on this from those in the know...
On the ECU compatibility front, this is an 2001 GTX RFI. Are DI and RFI ECU's interchangeable? Anyone know what year models span 2001 ECU compatibility?
Thanks.