U maybe going the wrong way. One reason your car could be slowing down is that your a little rich and humidity usually increases at night. Alcohol doesnt like humidity. Eventhough its cooling down the rise in humidity will offset the temp. try this.. go back to 160-164s and put a 28 jet on your high speed air bleed, you probably have around a 35 now, the high speed air bleeds are the ones next to your vents your carb. This will keep your engine alittle leaner out the gate for horsepower, which will keep your chassis planted and the smaller air bleeds will make your big end richer letting you keep your MPH.