If your engine light is coming on, your PCM should have stored a code to help in the diagnosis for the bucking condition.
It is puzzling that the dealer cannot pull the code. '94 and '95 are "hybrid" years for scan tools. The cars have OBDII connectors, but the PCMs use OBDI protocol. The tool needs to be able to connect to OBDII and read OBDI. A lot of confusion comes from this. But a dealer should be well aware of, and equipped to handle this situation.
You might consider changing out the PCM for a junkyard PCM from another '95 Bonneville. You should be able to find one for less than $50, and it is pretty easy to change. A properly functioning PCM should store and communicate the code that caused the engine light to illuminate.
In more ways than one, "what we have here is a failure to communicate."