I have a Gen 2 so maybe I'm missing something. I had a bubble in the heater core once. I think if you can park steeply nose up it might help.
It sounds like a bubble somewhere. If there is room keep adding fluid/running the engine/shutting it down and refilling and you should work it out.
2008 SE 4WD, Crew Cab, Long Bed; Leer 180 Cap, 2" Receiver hitch, Trailer wiring in bumper. Cooper 245/75/16 M&S (Winter). Cooper 265/75R16 ATP (Summer). Full set of Hefty skids, TJM Coilover w/HD spring, SPC upper control arms and 2" rear add a leaf plus 1" block. TJM extended travel rear shocks. Pyle backup camera wired to a Pioneer radio.