Thanks for all the great information. I am not really needing full automatic control, I have been operating the overdrive with a toggle switch for years. In the occasional instances when I forget to switch off the overdrive, I have come to a complete stop, then got the truck rolling again with it overdrive. Then I notice it and hit the switch, but no real problem. Not so with the lock up. So I really need just a safety to disengage it if I forget, or in a panic stop. I think one of those adjustible pressure switches would do the trick.