We are planning on installing 2.25" solid oak plank 3/8" thick with glue in an 11'x12" bedroom . The problem is the slab has settled causing a big crack in the center(too hight to grind), it seems the highest spot in the room is where the crack is. From the crack to the baseboard there is about a 1/4" drop on either side. Am I going to have to build up the subfloor all around the baseboard to be level with the crack? or should I scrap the idea of glue and go with a plywood subfloor and then staple down the plank. Is there an easier way that I am blissfully unaware of that someone can guide me with? Thanks for any advice you may be able to give

The specs for most wood floors are FLAT within 3/16" in a 10' radius. If your slab does not meet that, then you need to fix it. What about grinding the high spot down to better meet the the lower areas. Ask Perry (floorguy) who has tons of experience on slabs; 90% need to be fixed. Yes, it's a hassle. No quick easy fix that I'm aware of. Grind the high places and fill the low ones.

Gary is correct, as usual!

Grind the highs, and fill the lows