Whirring when WOT

I've got a '94 4.0 Auto with a 3" or 3.5" Rusty's lift RE adj. trac bar and ZY TRE. I do NOT have an SYE or TC drop so there is a slight vibe when coasting. The other day I went to pass someone and hit WOT and at about 2500rpm there was a loud whirring sound (almost sounded pneumatic or like a turbine winding up. Needless to say it scared the crap out of me so I let of the gas. For the next mile or two whenever I would accelerate the entire truck would vibrate :shiver:. Now She's back to normal for no reason. Does anyone have any ideas what would cause this? I was thinking maybe a band in the tranny but she shifted fine and there was no loss of power.

could be a driveshaft ujoint

it happened again twice today(I was trying to make it happen) and It only happens when I floor it and the trans downshifts. The whirring sound goes away as soon as I let up off the gas and it shifts up again. And the vibration from this is almost like driving on a very coarse gravel road. Also I forgot to mention I have a RE extended slip yoke and a brand new(not rebuilt) xfer case with maybe 5k miles on it.

Is it coming from the front or the back?

The vibration is literally the ENTIRE truck. The sound seems to be coming from the tranny/xfer case area but I know how sounds like to travel up and down the driveshafts. Definitely sounds like its coming from somewhere in the tranny tunnel though...not the axles.