my 2003 grand prix runs rough at idle and when i put it in gear but when its in park it revs up fine but acts like it has no power and is running on 3 cyl but i put it in gear and it wont go anywhere

my car runs like its runing on 3 cyl i can rev it up in park and if i hit the gas to the floor it will pop for a sec then rev up but it feels like there is no power ( its a 2003 grandprix with the 3.8L) then i put it in gear and it almost wants to stall( sometimes it does) and has no power whats so ever i was driving it and it lost all power i would hold it to the floor and it would bearly go but when im driving it and it runing like that sometimes it getts all its power back and run great for like 5 secs and then it goes back to runing like crap it shakes sputters when its in gear and when i put it in park it idles rough but i cangive it gas and it will rev up but just really weak.( i also changed the mass air flow sensor, and cleaned the throtle body out, changed the MAP sensor, and airfilter, and all the sensors on th throtle body) could it be the cat gumed up with a bunch of stuff? it seems to have little spurts of power sometimes but now its running like crap all the time i cant even get enough power to get up my driveway bearly please help me out with your guys feedback or comments i would appreciate it i need this car fixed asap its my only car, thanks.