Pzkpfw IV with 88mm....
Yes did exist in very very very small numbers (use 1 hand I think, all trials)
Hull cut down to just above trackguards, 88 placed on deck and two large sheilds that fold down to also work as the operating platform for the crew, gun is I think a standard Flak version.
This is from memory as my book on German AFVS is out on loan..
Oh yes... That Pz IV D looks great with one little catch, most Pz IV D where in Wehrmacht Gray (some exceptions in 43/44)