1991 Buick Century 91 Buick Runs then wants to stall

Engine Performance problem
1991 Buick Century 6 cyl Front Wheel Drive Automatic 116K miles

91 Buick Century 3.3L Auto. It starts right up and runs fine for about 5 seconds then idle starts to drop off. Sometimes it dies, sometimes it doesn't but it seems like it will stall any second. Putting in in gear actually seems to help it run a little better sometimes. When to temp it runs okay but just idles rough. Coming to a stop when it's still cold results in a stall half the time. I changed plugs and wires with no effect. The garage played with it awhile and said they finally caught the computer acting up so they replaced it. Now it hasn't stalled yet although it's trying really hard. But since the computer replacement, it lacks power and seems to have a miss. The miss gets worse the faster I am going or the more I press on the accelerator (never had this problem before). Pulling plug wires has the same effect on all cylinders so I doubt a coil or ign. Module problem. No idiot light comes on either. I'm assuming all parts and hoses are original.