Adding more income would make more of any Social Security you get taxable.  

@Trooper2 you can check the social security issue by reviewing the original return

Divide Box 5b by 5a.  if this is less than 85%, then adding the $20,000 to your income will add more to box 5b, so the result gets closer to or acheives 85%. I would expect that explains the entire $7,000. 

If Box 5b divided by 5a is already 85% before adding in the $20,000 then the problem is elsewhere. 

I assume you mean the column B amount on line 1. Compare the revised Form 1040 to the original 1040, lines 1 through 8a, to see which individual income items changed.

We are already at the maximum, but would that make the number in column B different, since it is referred to as the amount of increase?

Oops!  Nevermind!  It was the Social Security.  Thanks all, for putting up with me.