[thstone]

This is a tough one. I'm worried that the ECU fuel trims might be maxed out and even with the MAF disconnected this still causes the P0305 code. Try testing the MAF again by clearing the ECU first;

Disconnect the battery to completely clear the learned ECU fuel trim settings.
Disconnect the MAF.
Drive it and check the codes. You are sure to get a CEL for the MAF being disconnected, but we want to see if the P0305 returns.

If P0305 returns, then the MAF is ok and you're back to a problem that seems to affect only Cyl 5. If no P0305, its the MAF. Clean MAF, clear ECU, and monitor.