I Need to flatten a concrete sub-floor in preparation for wood flooring.

I have a 1953 ranch with a slab-on-grade sub-floor. The old flooring (recently removed) included: 12" linoleum tiles, glued-down carpet squares, and some slate flagstone. We want to unify several rooms with a glue-down or floating engineered wood floor. Unfortunately, the concrete is far from flat, with variations up to 3/4" all about the floors. I've tried many bags of self-leveling underlayment as well as concrete grinding (horrible mess!) but I'm afraid the floor is still out of spec (<3/16" over 10ft radius) and needs something more. There's about 1,200 sq. ft. of area that needs to be fixed.

Can I order a truck load of self-leveling underlayment and have it pumped into the house at a depth of .25" to .75"? Is that crazy? Cost-effective? Will it work?

Help please!