Choosing a stall speed.

The 2250-2450 brake stall I listed is out of the 1970 service manual. If its factory and stalling much more then that most likely the transmission is slipping (again at least according to the service manual). The other possibility would be the motor has been modified and making more power then stock. The 1970 340 converter has part number 2801764 the exact same part number as the 1970 225, 318, and 383-4 with a 727. In 1970 at least every 10.75 inch converter was the "high stall".