More info as I was just farting around with it-

coolant temp, oil pressure, volts all check as fine on the dash (yes I realize how GM dashes are notorious for being wrong).. I've verified they're damn close with a DVM for the battery/alt, mech oil pressure gauge for the oil, and the CTS (gauge sensor) is brand new. Also, I am running an electric fan setup using a BMW dual zone switch and aftermarket fan controller (SPAL, one each for the high and low circuits) running a dual fan, dual speed setup from a Dodge Intrepid. My cooling system is just NOT the problem, pretty much willing to bet any of you a bottle of fine Scotch on this one (thanks to Tom's extremely helpful input!).

TPS, IAC are questionable. Need to look into backprobing them since I can't get data out of the ECU.

O2 is brand new. It's positioned just aft of the joint where the banks come together in the y-pipe. This emulates the factory 5.7s of the era as far as I can tell.

I do not detect an odor of rich exhaust.

Back to the drawing board...