Help car feels like its braking by it self

First off, you should go check your transmission fluid to see if it smells burnt. Second, get driving and see if you can go real fast. If you get it up to around 80 or 90 mph, and the rpms are really high, then your transmission is bad. Basically it isnt shifting because it has been driven with really low transmission fluid or your radiator is clogged up causing the transmission fluid not to circulate through the transmission and cool down. On the bottom of your radiator there should be two little 1/4 inch or 3/8 inch hoses going into the radiator. Those are where the tranny fluid circulates through the radiator to stay cooled down. Your tranny is stuck in one of the gears. Mine did the same thing and stuck into third gear. I can drive and everything but the engine will redline at 90mph and you can put the transmission (automatic) into first gear and it will do the same thing as it does in drive. It will stay in the gear it is stuck in, but wont drop into first gear.