i have a 2000 gtp a couple of weeks ago my tranny started to whine and slip really bad so i replaced the fluid and filter right away. it drove fine after that for like 2 weeks then out the blue it started again to the point the car wouldnt even move as if it was in neutrul. once i turned off the key for not even a second it started to work fine again for like 2 miles, the car whines in all gears including park, the more gas you put to it the louder it gets, a trouble code for the toque convertor stalling came up about a month ago but everything seemed fine, what could the problem be? is there some type of dditive or should i just replace tranny?