Stumped

73 ohms brings the pointer up to the empty hash mark 80 ohms will not move the needle from the E. The oil and temp gauges are responding to 80 ohms at switch on as in 120 degrees or zero oil pressure by not moving if that makes sense. The fuel gauge should always respond to switch on by climbing from its home position to at least the empty mark.
If you have a sender that will make 78 or more ohms resistance at its empty stop, its flawed.