Just to close out this thread.
I purchased another main ECU. Huge difference.
Transfer case controls now work except LED'* were dead. Resolder board fixed that.
Drove over 200 miles on old computer and still 3 of the drive cycle readiness status lines showed "Incomplete" It then threw the purge vale wiring error again. I had never seen the catalyst test go ready.
After install, did the 30-minute "security procedure" to get it to run. Reset codes and drove it. Within 8 miles 7 of the 8 drive cycle status lines went ready. Next day started it and a minute later the last one, (O2 sensor heater test) went ready.
It is now throwing a "CKP System Variation Learn Procedure" code. The seller of the unit said that would probably happen and gave the steps to fix. I'll need to find someone with a scan tool advanced enough to send the learn command.
I bet when the previous owner swapped the engine and transmission from a Silverado, they also swapped the ECM. Probably from a 2WD so unit did not even try to talk to the TCCM and it expected different wiring connections and sensors.
Went to emissions test place and asked if it would pass with no emissions-related codes. Any error code will fail He also noticed the check engine light did not work (also a fail). I bet it is missing.
This has been frustrating. Spent 2 weeks on Craigs list and saw tons of scams and liars. Guess there are Liars, Damn Liars and Craigs List sellers
Sill with all the probs needed to be fixed, paid less than blue book.