Have 1994 Buick Regal GS I would like to know just what the vehicle speed sensor control, shifting or what?

the vehicle speed sensor is a monitor it tells u the driver and the ecm the speed of the vehicle and i monitors it for things like abs. the speed sensor will not control shifting on ur car as u have electric shift solenoids in the valve body not only does the ecm tell the car when to shift but line pressure inside the tranny tells the vehicle when to shift. see if u have a tranny leak of sorts from either the cooler lines or from the pan gasket. start the car and let it warm up to operating temperature like 195 degrees then check tranny fluid it sounds to me like ur tranny fluid is low or its been in the car so long that it is breaking down and is no longer viscous like it is supposed to be (viscosity= a fluids ability to flow) u might need to change the fluid but i would check the level first hope this helps