Occasional, slight burning smell and misfire on Stage II

[bluegecko]

I just had my car upgraded to a Stage II over the summer. Since I've got it back, it's generally great, but I've noticed an intermittent faint burning smell coming from the exhaust at times. It's not strong, it's intermittent, and it doesn't (in my opinion) really smell like what I'd normally think of as burning oil. More just…a faint whiff of something a bit burnt. The engine runs smooth, albeit it's usually quite rough with visible shimmy for a minute or two after cold start, and I think I'm hearing some minor misfires (and maybe a backfire, although it's a very quiet backfire if that's what it is) when I sustain past 3000 RPM. I feel like something off, but I'm not even quite sure where to start on this one; any thoughts?

I attached a recording, if that's useful; the volume can be misleading, but I think it's possible to hear what I'm hearing at least. I don't live anywhere near DMC Orlando (where I had the work done), so I'm really not keen on shipping it back there to figure out what's up if this seems like something I can take care of myself.