Backfire... Help!

[SharkPilot]

Had a backfire on start-up the other day. The engine stayed running but was rough as if there was a vacuum leak. We checked and found an oil swollen and loose hose to the MAP sensor. That was replaced with a new hose. We found the hose as the plenum was being removed. Everything down there looked fine. No hoses were off or even loose.
When it was all back together the idle was still rough and there was a really light surge at low speeds in 4th gear.
Since the oil swollen MAP sensor hose was found I replaced the MAP sensor, just to be sure. There was no improvement.
At work we hooked up a TechII and found the IAC count to be ~21. Shouldn't that be up around ~35 with the A/C off? I ran an injector balance test and there didn't seem to be a lot of change when #8 was cut out. I don't think it's the injector because with any kind of throttle the engine runs very smoothly and has all kinds of power.
Next we tried a smoke machine and found nothing. Then I went around spraying some cleaner at likely leak points and the engine RPM never changed.

As of this point I'm lost. I'm about 99% certain that there is a vacuum leak someplace that I just simply cannot locate. The idle has that "gallop" feeling that an engine with a vacuum leak has. The idle speed is normal but wanders around a little on the TechII screen so it's not a large leak.

Do any of you guys have any advice or ideas to offer me to solve this? The "Beast" and myself would be most greatful for any thoughts or advice.

SharkPilot