Maybe a dumb question, but is your car starting out in first gear? Ever? I have seen the wire to the kick down solenoid on the transmission go bad and you start out in second no matter what you do. This can be even slower than normal. If your 126 car has the position for first gear (put in second then move stick to right), put it in that position, start out and then snap it over to the 2nd gear postion at about 15 mph. If the transmission does not shift up, you already were in second. My wife's 107 has that problem right now and I just have to find the time to put the car up on ramps and find the bad wire.