What gasoline are you using??? (Brand and grade) and what tune??
i also have catted/res'd UR DP . ive supected a bad/clogged/ core push through cat issue. all which could cause misfires and off sounding exhaust notes.
going to scope it this weekend.
Vac lines maybe?
Always 93. I usually fill up in Mexico, when I started having this issue I used Chevron and made no difference at all.
I had a misfiring problem @ mid range. I changed part after part and couldn't figure it out!! I was desperate,, until one day I just started to backtrack and did realize that my problem started when I moved and was using the same gas station which happens to be a shell, long story short-I used a fuel system cleaner and now I'm using Mobil gas and no longer have the issue
If you are only misfiring on cold start up and runs good when warm it will not be your injectors.Tell them to clean the valves the proper way like allset did.