I have an 98 LSS with the supercharged engine and was looking for a company or person that can tune or modify the PCM? All the vendors that I have contacted say they can't do it. Is there anyone out there that can?

What mods do you have? You may want to PM "L67poweredLSS" He has the same car with a few mods. I know he has 3" down pipe and 3.4" pulley for sure. He may have other mods too? Not sure.

You're right. Not really supported, I only have a N/A 97 delta 88 file being relatively close.

Only one place does tuning for these cars. You have to get ahold of Ryan at Sinister Performance. That is the ONLY option you have. I had one of them, so I feel your pain!

Thankfully, Ryan is a great guy to deal with.

Well, not the ONLY option......

An alternative is to take the same year Bonneville file and do an entire write to your PCM, turn off the security, and tune that way. It's the same PCM so it won't be bricked, but the only issue is the PCM will of course think it's in a Bonneville, will have a Bonneville VIN number too. This might not be good if emissions testing sees a different VIN and fails you, so I'd just get a Bonneville PCM and keep your factory PCM to use for emissions only.