Chassis dyno graph

Rhett, this is how I test for stall speed.

If your car still shifts automatically and uses the kick down linkage, disconnect it for the test.

Drive slowly and let the trans shift into high gear.
Go along slowly at around 1000rpm........push the throttle to the floor and observe what rpm the tac needle jumps to and first stabilizes at.
That’s the flash stall speed for that converter behind your motor.