Thanks, JagV8. That's what I'm thinking. I plan to replace the 02 sensor on that bank and see if that helps. If not, it must be the cat. Don't know if I'm going to fool with that since it is OK under all other conditions. Don't want to spend a lot of money before I sell it. Haven't decided.
Thanks again.

 

Replaced both cats today. On a space limited test run, no more issues. No misfires of any kind, no codes, ran out of room to continue.