Thanks Jerry. As far as I can determine, the lockup is working correctly. Its definitely locked up at speed and releases when I touch the brake. I have about 10-11" manifold vacuum at constant 75 mph and the power piston spring is set to start to lift the rods at around 9" vacuum. I might try a still lighter spring but its got good throttle response now. I temporarily install a vacuum gage in the cab when I do testing and it is very revealing to see how sensitive the vacuum is to small changes in the throttle. I've probably wasted more gas just doing the testing than I will ever save.

Mark