Runs but cuts off and gets to 40 45mph, but won't go any faster?

When I first drive it, it will start changing gears, (somtimes) but after a couple of mins. it will stay in the same gear, feals like 3rd gear, I have jumped started this car many many times, I was told that if I take the positive off the battery while its running, and it cuts off, I have a bad alternator, is this true? I was also told that my alternator can affect the shifting of the gears, is this true? I have actually had the car cut off on me while stopped at a stop light. When it gets to like 40 or 45 mph, it will not go past that, it will actully rim up like if I had it parked and just pressing the gas?? The check engine light is on. I have had it sitting for a while, like 3 1/2 months, it is also leaking trans fluid, I do know that it has had a trans leak for a while, I got a new gasket put on the trans plate but it still leaks, I think one of the screws is stripped down there or somthing, could this be the problem? What do you think I should replace first, or what should I do alltogeter? Please help me out with this I need to get it on the road as soon as I can, I have a family and we need a socond car.

THANK YOU :-)

did you check the codes that the check engine light is giving ? if you dont know how, check out this link.http://www.stratusphere.us/forums/i...p?showtopic=124 (http://www.stratusphere.us/forums/index.php?showtopic=124)

don not take you Positive terminal off when the vehicle is running, the voltage spike induced when you do this could fry your computer... Many people have different opinions about this but i would not recommend to do this.

does anyone else no what is wrong with my car?