I had the same problem, the dash would "float" up and down.
There is a simple fix, just push the dash up a little from under the hood
and squirt a little "great stuff" expandable insulation under the dash from under the hood. The great stuff will expand as it dries and will stop the dash panel from moving. Do not use too much or it will oooz up between the dash and windshield as it dries. Have some solvent ready so if it does you can clean it up before it dries, the instructions on the can says what kind of solvent to use. Be careful if u have to clean any up off the dash as the solvent can damage the covering on the dash if you do not use it sparingly or rub too hard. If any sticks out after it dries it can be trimmed off with a knife.