2000 Grand AM vibrates

I lately bought a 2000 Grand AM with 4 cyl., 2.4L engine. It has 64000 miles. The car runs smoothly. When in the park it vibrates a bit. I can live with it, it's minimal. But when I put it in the drive gear or reverse one it gets worse. The whole car has this symptom, including teh steering wheel and the exterior left mirror. It gets worse if I camoe to a stop on the uphill or downhill surface, even a slight one. But when the A/C is on it gets even worse. It drives me absolutely nuts!!! I had the following performed:
-wheel aligment
-wheel balancing (brand new tires 225/50R16)
-engine mounts checked (all are fine)
-spark plugs and the "wires" changed - that actually helped noticebly, but not that much, not to my satisfaction
-new front rotors
-new porcelan brake pads
-something else cleaned of gunk, I don't remember what.
-belt tensioner and belt changed
Two mechanics told me these engines are crappy and they always shake. But I drove a rental with the same engine and the ride was awesome! I am ready to sell it but who will buy a shaking car?
The idle speed is at 750rpm so I think it's OK.
Anybody has any suggestions? I tried to google but I cannot find any other solutions except the ones I already performed. PLEASE HELP or I WILL go bazooka on this piece of crap!!!
Thank for your time.

check your harmonic balancer/lower crank pully and make sure it is not coming apart. also check your pvc valve and egv valve. could also be a intake or vaccum leak!

I will check for these things. Also I forgot to mention I have oil collecting in the bottom of the intake tube. Do you know what the cause of that could be? Could it be related to the shaking?

the pcv system is the culprit for the oil in your intake tube. IF it is plugged, it will cause excessive pressure in the crankcase, which will lead to excessive oil consumption and even possibly the vibration you describe.