I recently experienced strange behavior from my 72 Riv. When I tried to accelerate onto the freeway the engine lost power and then started surging back and forth as if I was losing fuel. I back off, eased into the power and she recovered, but the shifts started to occur at high rpm and were hard. She idles fine and drives ok except for the high rpm/hard shifts. I was going to check the vacuum lines and modulator... any other suggestions? Thanks
A vacuum leak to the modulator, or a defective modulator will make the transmission think you are at WOT, increasing line pressure and making for delayed shift points. A vacuum leak will also lean out the fuel mixture leading to performance issues. Inspect carefully the metal line and vacuum hose at each end of the line for cracks/leaks. Take the modulator off and point the vacuum nipple down. If any ATF comes out of the vacuum side, the modulator is toast. If the modulator will not hold vacuum, it's toast, replace it.
