Stumbling woes continue.. what's the next step?

[Thieu]

Okay so as many people do, I have the stumbling problem at idle. It just sounds like the engine is sputtering and the exhaust burbles a bit. If I manually rev the engine a little under the hood, the engine shakes a lot (slight load) and it skips/sputters a bit if I just hold the throttle open at a certain point. I've changed just about everything under the hood that could have to deal with this except for the FPR and the fuel pump.

I just went to the junkyard and got another air regulator yesterday and a new connector for it. My AIV/EGR are removed. New injectors, fuel filter, everything ignition related is recent. I've replaced the IIC, PCV valve, cleaned the inside of the intake manifold and the throttle body, and I've redone all the vacuum lines.

I'm just at a loss.... should I go ahead and try a new fuel pressure regulator and/or walbro fuel pump or run seafoam?

This stumbling at idle is annoying the crap out of me...