when was the CS set? Has there been a change in financial circumstances (my stater 3yr or 15%)

If you want to modify the parenting plan (tax/time/custody) you are going to have an uphill battle b/c you have established status quo. He can pretty much do anything he wants during his parental time, including taking child to grandparents. The only legal leg you MAY have is the moving in with his g/f as that is specifically contrary to the parenting plan.