Setting any codes? I'd check fuel pressure too with key on-ignition off then running just to rule the fuel system out too.

Sounds like an ignition problem, that would be the most common over TPS, MAF or IAC, IMO . Check the car running at night or in the dark for any random sparking or arcing? I'd bet one of the coils or the ignition module from the sound of it. I upgraded my LeSabre to the Delco II ignition (same as your Regal) and have some spare coils and modules in my car with tools just in case. Overprepared or paranoid I know but those would probably be the first things to go. Not common I'd say but I'd start there first. Modules can be tested at auto parts stores, not sure on coils.