So about 3 weeks ago I was driving and something like stopped working and the brakes slammed on real hard by itself. Afterwords I stop the car put it in park and turned off the car check under hood and under car and seemed normal to me. After that I start up the car and put it in drive and it won't move it just stays still as if it was in park so I step on the gas more and it goes but slowly like 5 mph and you hear this clunk comming around the motor when it moves a couple ft forward. Don't hear the clunk when it is reversing though. What could be the problem. car only has 85k miles and I change oil filter and oil at 84k too so I don't really know what the problem is I am assuming that it is the tranny but what do you guys think any opinions?