Quoting: F Body
Having a look in my GM Manuals
According to the Official GM Service manuals ( all 1,187 pages of them ) Most electrical faults should throw a code and/or illuminate the Engine management light, therefore I think your on the right path thinking fuel related.
Check the intake system for a vacuum leak which may cause a misfire.
Damaged/worn vacuum hoses.
Loose or split connections around the MAP sensor.
MAP sensor sealing grommet.
Throttle body gasket.
After that it gets more difficult & expensive :
Warped intake manifold.
Warped of damaged cylinder head sealing surface *
* I'd be expecting some sort of coolant loss and/or oil contamination.
Pull the oil filler cap and check it's not full of mayonnaise.