You can try tipping the pinion up 1 degree more, 2 degree is sort of the lower limit on the static angles. With the slip yoke out 1" farther, it may now be a little looser with less spline engagement, do you feel any play when you grab it and give it a tug? Also, are the u-joints in phase exactly? If they are lined up, one option is to pull the shaft apart and spin one half 180 degrees and put it back together. Sometimes there is a slight variation in the phasing that works better in one orientation than the other. Also, try painting the slip yoke splines with grease (vs. just squirting grease into the zerk - into which you don't want to pump too much). Also, any play at all in the flanges? I often find vibes when backing off the gas are due to something being loose, when you unload the driveshaft, it gets into that loose area and vibrates. Also has the shaft been balanced recently? A small scrape or dent can throw it off and with the added operating angle you picked up with the lift, what may have been indetectable before has now been pushed to the point where you can feel it, BTDT. What is the overall angle on the shaft itself? I found somewhere between 12 and 15 degrees on the shaft is about the limit of smooth operation with u-joints.