You were right. I pulled the T valve out and completely dis-assembled it. Under a magnifying glass there was a small amount of debris inside. Don't know what it was. O rings looked good. Cleaned it real good in solvent. Also cleaned the rest of gun again. Air dried, oiled, and re-assembled. The first 3~4 shots it multi-fired like before then it started slowing down and getting better. After a dozen or so shots it was single firing. It will double fire at 20 or so hits, but It acts like it will be ok with some use.
Thank you very much for your help and persistence on the trigger valve. Larry