When vacationing this summer in Myrtle Beach, SC, I noticed the City went along the sidewalks with a concrete grinder to even the edges where roots had pushed up a slab of sidewalk. I looked to be very effective since the borders of slabs were even, although the slabs may or may not be level due to the roots. An I'm sure that is a cheaper solution than breaking up the old slab and pouring a new one. Haven't seen this done around ABQ, but I would like you to consider it. And I realize it won't work with all of them. The one in the picture was pushed up so far that it may be the thickness of the slab above the other slab.