What would cause a severe loss of power to engine and abs light and bouncing speedo all at once It's on a 1999 GMC Savana 5.7 with 170k I have seen about 3-4 other people post but no answers?

A severe loss of power, along with the ABS light and bouncing speedometer in a 1999 GMC Savana, could indicate a failing vehicle speed sensor (VSS) or electrical issues such as a bad ground connection or a failing ignition switch. Additionally, problems with the engine control module (ECM) or issues in the wiring harness might also cause simultaneous electrical failures. It would be prudent to check the sensor and wiring for any damage or corrosion, as well as to run a diagnostic scan for any stored trouble codes.