I have a 2006 chevy silverado 4.8L 4x4 automatic
transmission. What years and vehicles can i get a
used replacement from?
You really need to identify the transmission type (model). Then look for comparable models. I would recommend steering clear of used transmissions. The amount of work required to install will double if there are any problems with the used transmission.
GM is very specific about their transmissions, you need to get the number off your bad tranny and then look for a transmission that matches that number, if it doesn't match then it won't work even thought it might bolt up. Gary is right about used transmissions, rebuilding yours is the best thing as long as the case is not damaged.