Hey guys,
My dads 2000 Chevy Express Van (5.7) sat for a few months and then started doing some crazy things.

The gauges read whatever the hell they feel like. Speedo is like 3x your speed, and the ABS light is on.
First I thought was a speed sensor, but changing it did nothing.
My only other idea was maybe the PCM took a dump on him? But wouldn't that throw a code? The car is throwing no codes, and shows no CEL.

Heres what I've done:
Removed neg cable of bat and turned key to start for 30 seconds (flashed ECU) No change.
Replaced speed sensor on the tranny. No Change.
Checked all wires under hood and from the VSS. They all check out fine.
I think the problem may be related to the ABS switch/sensor/relay so if anyone knows where any of them are that'd be great. The fuse box under hood says "ABS Export" but theres no relay there?

Any help would be greatly appreciated!