hi. I have a 72 mav with a 302 in it. and at highway miles i.e. 55 to 60 mph I get really bad pulsation vibrations in my seat. but if I drop it down into 2nd gear it doesn't vibrate. would this be a problem in my transmission or a mount? hopefully it's not anything that will kill the bank account. anyways any thoughts are appreciated. thanks
nick

I had something similar on my 76
It would vibrate on load, it ended up that the needle bearings in my u-joints(driveshaft) where gone (literally)
raise the car and check for slack on the driveshaft.