more good news! follow up. i went down and picked up another drive shaft, a rear diff, and rear axles from one of my parts cars. i grabbed a drive shaft with 3 u-joints instead of the one with a cv. that was the first thing to be replaced and the high frequency vibration is gone!
kinda sucks cus i had around $300 in rebuilding the one i took out
. so either u-joint replacement done wrong or bad carrier bearing. maybe i'll put the new u-joints in the new driveshaft later, for now i'll just enjoy the smooth sailing. i'm just glad it's over, thanks for all the input fellas.