I WAS DRIVING AT 65 MPH ON I-476 (PA), WHEN I SLOWED SLIGHTLY TO CHECK EXIT SIGN. UPON DECIDING TO PROCEED TO NEXT EXIT, ACCELERATED MIDLY FOM 60 TO 65. TRANSMISSION SLAMMED INTO, WHAT FELT LIKE, 1ST GEAR CAUSING VEHICLE TO PITCH FORWARD. THIS WAS SO SUDDEN, THAT IT THREW MY HANDS OFF THE STEERING WHEEL AND CAUSED ME TO ALMOST LOOSE CONTROL OF VEHICLE. HAD SOMEONE BEEN BEHIND ME, THE ROAD BEEN WET, OR HAD I BEEN ON A CURVE, I WOULD NOT HAVE BEEN ABLE TO REGAIN CONTROL. TRANSMISSION SHOWED SIGNS OF POOR SHIFTING BEFORE THIS INCIDENT, SO I TOOK THE VEHICLE TO ACURA. THEY FAILED TO FIX THE PROBLEM. I WAS VERY LUCKY, THIS CONDITION COULD HAVE CAUSED A MAJOR ACCIDENT. MR