^yup. GM MAF is waay outdated. You said you had an SAFC....did you make sure you successfully reattached the MAF wire? I dont know how the GM mafs is hooked up so I dont know if this is at all relevant...

That happened to me when I swapped my engine...I pulled the SAFC and sold it like a month before I got the car ready to start, and the bitch wouldnt stay running at all lol. Turns out I just yanked the SAFC and forgot about it.