Wireless networks in the immediate area are what cause a wireless camera to not function as well as wired.
I can offer a suggestion, although in part it defeats the purpose of a wireless system. By moving the transmitter as close as possible to the monitor will solve most if not all problems. I cut & spliced both the camera cable & power cable making each one longer. My wireless transmitter is now within 5' of the monitor & everything works perfect.
I ran the cables along the frame rail of my truck using wire loom & up between the bed & cab.
just a thought ;)