Battery dead short to frame

Welcome to 2CarPros. With that description I would start with the negative battery lead, then the grounds from the body to the frame as well as from the engine to the frame. Look for corrosion or actual burnt wires. Because of the short I would suspect a body ground first but all of the wires were under a very high load. If the engine was running at the time it may have also cooked the alternator.

Good to hear. You may find other things after it runs a while depending on what did or didn't pass power through it at the time. I have seen a shorted battery do some nasty things because of the amperage involved.
Changing the range sensor isn't hard if its the common automatic transmissions used. Jack it up and secure it with the drivers side higher if possible. That moves the fluid to the opposite side. Then unscrew the sensor. From the case. Next shift the lever Between reverse and neutral while looking into the hole the switch goes in, you want to check that the finger inside is in the center in both gears. Put the new seal on the switch and install it. Tighten to 25 ft. Lb. Reconnect and verify switch works properly.