Ya, HPT credits...what else you gonna do with them? Have you read the OK tuned pcm and saved it?
I don't know if you need to update the VIN in the OK pcm. If it sets off a security code/lite or the radio and things don't work, then I guess so. I would try running it with the OK tuned pcm as is. The GT trans is 3.29 geared like your old setup. Not sure if the valve body difference deal matters in this swap. What about test-running it on jackstands?