With the correct stall for the engine, usually a couple hundred over peak torque, you should pick up 1-3 tenths. Weight savings and lower HP loss through the glide more than make up the difference. The glide also seems to work the converter for a little more to add as well. An easy test is to footbrake the car with all 3 gears, then try it starting in second. If it runs no more than a tenth slower 1/4 mile the glide will be better. We ran TH350's years ago, by accident we found starting in second the car ran about 2 tenths faster. Switched to a glide and picked up more. This was in 11-12 second cars.