@lostinfla just replaced my whirlpool in August.
1. Unplug microwave and remove header panel above microwave door. Two screws on top of panel.
2. Newmar cut away portions of the grill behind the header panel. You should see the heads of five #2 square headed screws no longer than an inch or so. Remove all but two located in center.
3. Remove grease filters from under microwave. Should see one #2 square headed screw located on rear of each opening. These are three inch screws that are screwed into back support panel. Both can be removed as the microwave is resting on wall support bracket. I think these screws provide support to keep the microwave on the wall bracket as you drive on our rough roads.
4. Place cushioning under microwave to protect cook surface/counter.
5. Pull electric cord through hole in cabinet.
6. With help of another person or persons support under outer edge of microwave and remove remaining two screws located in step #2.
7. Let front of microwave carefully swing down while pushing upward on rear underside of microwave to detach the microwave from the wall bracket.
You might know that when installing microwaves in a house the top front of the unit is secured with two or three wide-headed bolts installed thru the base of the above cabinet. Newmar has placed a decorative panel above the microwave. This panel is mounted with double backed tape. I carefully removed the panel by using a plastic putty knife. This provided access to the front cross member to drill and install the manufactures mounting bolts rather than having to carve up the grill of the replacement microwave to reinstall the screws Newmar used to secure the unit.
You might be lucky and the new wall mounting bracket may matchup with the old mounting bracket. I installed a Bosch unit and it did matchup.