No engine power

I have a 1997 Intrepid with a 3.5L V6. My engine seems to be bogged down and the vehicle wil not accellerate quickly. It seems to shift fine and runs good when it gets up to speed, but getting there is a real bear.

I have had other problems with the car that have been repaired, but these seem to be unrelated to my current porblem. Several weeks ago, the car stopped running all-together, It would crank over but not start at all, it was not getting spark. Through trial and error, I replaced the coil pack, the camshaft sensor, and finally the crankshaft sensor, which fixed the problem.

The car ran fine for a week, then out of no where, on the same tank of gas it had been using all week, it started running really rough(sputters/missing) when the vehicle got up to operating temperature.

I checked and double checked all of the sensor connections, including the ones that I replaced. I checked plugs and plug wires, I am getting spark, but I went ahead and changed the plugs and wires anyway. No engine light comes on. I was advised that it is most likely the fuel pump, so I replaced that too, that didnt work. I ran a tank of fuel with a cleaner through it, that didn't work.

I took the car to a garage to have it fixed, and three weeks later, the mechaninc had ran diagnostics and found nothing wrong, he looked at the timing belt and said that it was fine, and he replaced the intake manifold gaskets.

After three weeks and no progress, I went and got my car back. Now it seems to have gotten worse, it didnt cough and sputter when I left the garage, but did not have any power. It feels like the vehicle has no compression, I thought it may be a blown head gasket, but I checked my oil and found no signs of coolant in the oil.

I cant find any vacuum leaks.

I cant think of anything else I can do to describe the symptoms any better. So to sum it all up, here is a list of what the problem most likely isn't.

Camshaft Postion Sensor
Crankshaft Position Sensor
Coils
Plugs
Plug Wires
Intake Manifold Gasket
Timing Belt
Fuel Pump
Bad fuel

No Engine Light on

Thanks for any help, folks. I'm really baffled here.