You might check the engine wire harness, particularly at the AMM connection on the driver's side fenderwell. I had similar trouble earlier this fall, on my '85 245 with a non-turbo B-230, AW 71 tranny, which would stall whenever shifted into reverse. I found the connectors in the harness AMM plug and the AMM terminals dusted with a white precipitate from a recent engine wash with a power wand. Cleaned both sides of the connection with a toothbrush and contact cleaner. End of problem. Apparently the leg of the wiring harness which serves the AMM would swing enough with the torque of shifting into reverse (or a right turn at slow RPM) that an already iffy connection was compromised. Braking, I assume, could cause a similar pull on the harness leg.