Our 95 Transport 3.8 had a slightly rough idle for several years, and I
finally took LMP's advice and changed out the ignition module because of the age of the car. He STRONGLY believes it is important to change out the ignition module AND the crank sensor after 10 years on a vehicle.
I bought an ignition module that had new coils attached on ebay for cheap. The odd thing is, the slight miss at idle was gone. Period.
My 3800 GTX has alot of mods, including a 150 hp nitrous, and I had some bogging on right turns, which finally got worse, and I replaced the dual platinum plugs with another set of Autolite 103AP.(4 heat range colder)
To rule out the fuel pump they say to tape a fuel gauge to your windshield, and drive the car.
Upon reading the first few lines of your problem, I was strongly thinking the ignition module. (obviously you already checked your plugs and wires first?)
KEV-just something to think about