VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 400 cid stalling @ road speed

My '71 Impala 400 cid auto has started stalling whenever it gets to 40 mph and shifts into high gear. Changed the fuel filter, but now think it's behaving like its something electrical. It happens everytime I get to 40/45 mph, stutters real bad, sometimes even shuts off. If it shifts back into 2nd gear it runs again just fine. I can only start it when I pull to the side of the road and put it into park; but it starts right up again. Idling in the driveway is perfect. Also, acceleration from standing or from 1st to 2nd gear is excellent. But, get to 45 and it virtually shuts down. Also, idles strangely (like its struggling for gas) when coasting to a stop sign, or waiting at the sign. Any ideas?

Not aware that '71 had them but know that '72 and later had a TCS (transmission controlled switch) that kept the distributor from advancing until in high gear. Suspect that this is the root of your problem and is related to the distributor advance. In most cases people just bypassed the switch by routing the vacuum hose directly from the carb base to the distributor and not with the switch in between.