shifts smooth 1st and 2nd gears stalls in 3rd but go into passing gear fine

Hello, Sounds like there may be an issue with the overdrive solenoid or the torque converter clutch lockup solenoid. If one of these are the culprit, they can be diagnosed very easily with a professional scanner by commanding them on/off and monitoring transmission function. There are some other possibilities, but again, you really should have it plugged in to monitor operation before deciding on a repair strategy.