I recently purchased a foreclosure, removed carpet and marble and have discovered one of the main beams running the length of the home is high making the sub floor "not" flat. It begins in the entry and runs through the living room. In some areas my sub floor is "not" flat say 1/2" - 5/8" over 4-1/2 - 5'...so its quote a bit. The other side of the beam is not too bad and I can fix with leveling compound or shingles. I was looking for some advise on what to do to fix that amount of difference. I could remove the sub flooring (all tongue and groove) shim it or plane it and put new sub flooring down. I believe its too much to sand. I want to put down 3/4" x 2-1/4" hardwood but know I have a lot of work to do on the sub floor. Any advise would be greatly appreciated. I do have mostly suspended ceilings in the basement so joists are accessible, however the support jacks are encased in a wall and the beam has a drywall ceiling built around it.

You can either shim the floor and add another layer of plywood, or take up the subfloor and plane down the joists as you suggested.