My transmission "expert" replaced the thyristor and then the transmission computer modulator with no success. I gave up and I simply start my truck and warm it up before driving it. The thyristor's job is to not allow the transmission to engage or engage at a slow limited driving speed because it detects temperatures low enough which can jeopardize the transmission with increased transmission oil viscosity at low temperatures. However, my problem starts at only about 35F instead of about -30F.