Severe Vibration At Low Speed Acceleration

Need some ideas for where to look. This just started up last night on my way home from work. Here's the situation:

For the previous month or so, I've had a subtle squeek coming from what I would guess is the u-joint of the driveshaft at the t-case. I am not 100% certain but this was where the sound seemed to originate from. Only occurred when I was like backing out of a parking spot or creeping through a parking lot. Checked for play in the driveshaft and wear on the u-joints but found nothing.

I was stopped at a redlight yesterday and when I went to accelerate, a horrible vibration started up. I'd compare it to driving on the shoulder of some interstates that have the grooves (I call them wake-up bumps). I mean it shakes everything. Again, it seems to originate around the t-case to rear axle area. It's so violent it's hard to pinpoint.

If I creep off the line, it either doesn't do it or it's so small it isn't noticeable. It only gets bad under decent power and only shakes up through around 25 mph. Then it smooths out and no problems at any other speed.

It is not affecting the transmission as the shake continues through the shift from 1st to 2nd gear (auto). No slippage in the tranny. No affects on the motor. Seems entirely related to speed/driveline rotation.

So what am I looking at/ for guys? Bad u-joint or something worse like t-case damage? This is my DD and ONLY vehicle so I can't risk being stranded or without.

Need help asap!