My gauge cluster has been cutting off at high load and/or boost. However, if you turn the car off then on, it works again until high load.

This all started happening after I installed my new Kaaz diff and was doing figure 8's in the parking lot and my rear mounted battery fell over. When it fell over, the gauge cluster turned off.

Things I've checked:
Battery terminals - I've cleaned them and sanded them.
Battery grounds - I checked those and even added 1 more.
Solder Joints in the Cluster - I've resoldered every single one of them.
Engine Bay Grounds - I've checked these also.

I have a drag race this weekend and I need to my tach to be functional. Im pretty desperate here. Any input would be greatly appreciated.