1982 Chevrolet Blazer Transmission

First pull the hose off the vacuum modulator when the engine is running and be sure there's vacuum on that hose. If there's not, check for a leak. That will make it look to the transmission like you're at wide-open-throttle, so the up-shifts will be at very at high speeds. Check for transmission fluid leaking from the modulator valve. That will cause shifting problems, loss of transmission fluid, and black smoke from the exhaust.