I don't know much about cars or how they work, however lately I think I have been having some transmission problems. Everything works fine, until I hit about 45 miles an hour. Then my RPMs jump to 3 or 3 and 1/2 and the accelerator becomes hard to push. I also hear almost like a grinding noise that sounds like it's coming from the engine. It's hard to get the car above 50 or 55 without feeling like the engine's going to fall out. The car drives like it's in D2 or overdrive, but it's not...?? Any ideas as to what the problem could be?