Before you start beating up thing's , test the electrical circuits. Do you know anything about automotive electrical systems ? How to use a volt meter an a wiring diagram to test for B+ power to the switch an testing the ground .
Does your envoy have memory seats ? Your vehicle has four or more electric motors to control back an foward , up an down etc.. the odds of more then one motor being bad at one time are highly unlikely .
Look under the seat any trash under there keeping it from moving ?
If you have memory seats there is a control module involved in making the seats work . If it has memory seats it could have DTC'S - diagnostic trouble codes .
DTC B1735, B1740, B1745, B1750, B1755, B1760, B1815, or B1820
The seat adjuster switches are inputs to the driver and passenger seat modules. The seat modules supply the adjuster switch assemblies with a battery positive switch supply circuit and monitor the switch signal circuits. In an inactive state the switch signal circuits are floating and when a switch is pressed the signal circuit is closed to the switch power circuit within the adjuster switch assembly. When battery voltage is present on the switch signal circuit the seat module determines the switch status to be active.
DIY Blazer GMC Jimmy Power Seat Control Diagnostics and Repair Electric...