Chev van electrical issue

I have a 2005 chev express that developed an electrical problem. Out of the blue one morning.

the speedo fluctuates 20 km either way of actual speed, ABS lights and bells ring, transmission shifts from drive into neutral and back into drive(continuously shifting). All happening while driving.
when stopped at a stoplight. All alarms stop. As soon as you accelerate. It all starts happening again.

The battery is draining overnight.

It is definitely a bare wire somewhere. Not sure where to begin looking.

I have to believe out of all the chev vans produced someone else has had a similar problem.

Any help would be appreciated.