PCM Diagnostics & Tuning - Bad gas mileage

Hey guys. I recently sold my bolt-on SS and bought one that was cam'd and tuned by Speed Inc' back in 04. It has pacesetters, ory, Corsa (that I just installed) and a baby cam; that's it. Why would I be getting 15-17 mpg's? Highway and city driving vary, but only slightly. I'm hoping it's just in the tune so I plan on going to Mayhem Motorsports in a few days to have them do it all over. It does smell a little gassy, but I thought that could have been the absence of cats. I changed the plugs and cleaned the maf but it still can't get over 260/ tank. How hopeful can I be for the tune to help?

It depends on the cam. The more overlap you've got, the worse fuel economy you're going to get. Plus if it's an auto, it's probably got a converter. That won't help things any either.

If you're sure you have no exhaust leaks (especially upstream from the O2's), you're probably not going to gain a lot from the tune.