Vibration at 25-50mph

Ive got a 99 tacoma x-cab trd etc, with the 4" pro comp lift, and also 2" fabtech aal's. I am running bfg a/ts 33x12.50r15's on eagle alloys 589's (15x10) with 4.25 backspacing. I have had vibrations and shimmys in the steering wheel since i lifted it last may. I have always thought it was the tires, and have balanced them myself at work, had them balanced by the store i bought them from, and also speed balanced ($75 each time!! (3 times!!)) at a tire specialist, a total of probably 8-10 times. I even had BFG replace 2 tires because they were somewhat out of round. Anyways after all this my vibration has got alot softer, but is still anything but gone. I feel it most from 25- really bad at 35-45 and on through to about 50, then it goes away. I know the offset of the wheel could cause some of this, could this be all? also it seems to get worse after time, like they need to be balanced again. I also have read alot on here about shims i could put in (either carrier or under the leaves) but i know that my blocks from the pc lift are tapered, what do i need to do to correct that other 1.5 -2" the aal's gave me? This is about to drive me completely crazy, so any input will be greatly appreciated. Thanks again - Tyson