[79BIG10]

Kelly's right. It sounds like the vaccuum tube that connects at teh back of the intake manifold behind the carb then routes down to teh passenger side rear of the tranny. Look for the small pipe and also check the rubber connections for leaks. If they look good and not leaking the modulator needs replaced. It's the brass or silver looking connection at the tranny that the tube connects to. This is the part that is controlling the shift points. If you get a new one it may be adjustable. If it is you will see a small screw inside it. If so then to make later shifts tighten if sooner shifts needed loosen.