Intermittent Poor Running
 

This is regarding a MY91 engine transplant. Problem started occurring maybe once every 4-6 months but has gotten progressively worse. Would randomly start running extremely poorly with an occasional backfire on decel. Sometimes right at startup and other times a fully warmed engine. If I let it sit for a few hours it would self-correct and run perfectly again. Recently took a turn for the worse so it's parked now.

Checked a number of things including the AFM, CHT sensor, Ignition Coils, DME relay and the OX sensor was replaced 2 years ago. The spec for the speed reference sensor is 960 +/- 96 ohms. My reading is 577 between pins 1 and 2. No reading between Pins 1 and 3 as well as 2 and 3. This doesn't seem right?

This thing looks like a real PIA to change out so want to make sure. Thanks,