Pontiac Repair: 1995 Grand Prix Misfire & Now Wont Start, grand prix rough running

Question
My 1995 Grand Prix 3.1L was stored for 6 months with 1/2 tank of gas & ran great before. It has 200K miles. I started driving it again but it ran rough on start up, bucking a bit going up hills. I assumed water in the tank & used Berryman's B-12 thru 3 tanks of gas-no change. It was worse the faster I went - at 50mph or less, it ran a bit better.
One day driving to work it suddenly shuddered, ran very rough at all speeds & idle. It also had a throaty, rough exhaust sound (popping occasionally) that it did not have before. This happened just all of suddened, no warning.
I changed the plugs & plug wires & tested the ignition module at O'Reillys (tested OK) but problem persisted. I left O'Reilly's & it still ran rough but started shifting gears very hard. Suddenly it bucked hard once or twice & died. I had gauge lights & it cranked, but no restart. Not sure if coil packs got back in right order on the ign. module. Plug wires are on correct coils electrodes. Car still won't start.
I then replaced the fuel filter and all 3 coil packs. Now when trying to start, it acts like it's out of gas. I put 4 gallons in, so I know it's not. It will crank & turn over, hesitate, & I hear an occasional muted pop from the tailpipe. It intermittently tries to catch and fire up, but never does. I can hear the fuel pump hum for a few seconds when I first put the key in and turn ignition to 'accessory' or 'on'. Any ideas? Help!

Answer
Hi Shane:

I would start by checking the fuel pump pressure just because you hear it running doesn't mean it has enough pressure to run. that engine needs 40+ Psi to run okay. if that is okay thne next check for spark on the cylinders. If not that then maybe you have a fule delivery issue withthis car either plugged injectors fro the cra sitting with possably bad gas or maybe you have an issue where the engine computer isn't running the injectors.. If you live in the rust belt like I do I'd look at the engine computer. It's on the right side under the hood under the fuse box take a look at the computer and see if there is any corrosion in any of the connectors to the computer.
Good luck :)