Yep, exactly what I was trying to say without knowing the actual specifics on the cams/converters (I haven't owned an LS1 in 5 years and mine was an M6 and never cammed).Most people dont pick the right converters for their cam/setup....
Most F-Body guys run the Yank ss3600-4000 which is a good converter but is more efficient off the line and not as much on the top end.
The PT series is a lot better on the top end. I wonder what kind of stall [ brand ] he has. Also, a 3600 isn't enough stall for the cam that he is running which I think is a factor in you beating him...