i have a 67 mustang with a or what I believe to be a 76 model c4 transmission. It has a dual modulator valve on it which i believe is for an egr vehicle. can I just plug the second hole or do they both have to b hooked up to vaccuum to work and what exactly does it do. My tranny doesnt slip but it seems to stay in neutral for a few seconds before changing from second to third. Someone told me it may be the modulator causing the problem. If anyone knows what its actually for and can explain its workings it would be greatly appreciated.