My 02 blazer would only click and barely turn over at all I put in a new battery and changed starters with another used one. Does the same thing. The motor only turns over very little then only clicks

Double check the ground straps and cables. Anything that the battery and starter is connected to, inspect and clean.

If all your connections are clean and good and it still barely turns over, check the battery for a full charge. Make sure it is hooked up correctly. If the battery and connections are good correct and clean, remove the spark plugs and see if the engine will turn over freely w9ithout any pressure on the combustion chambers. When you say you just bought "it" do you mean the truck or starter. It very well could be the starter if it is a rebuilt one. Bad bushings or armature. It has happened. Have both the battery and starter put on a bench and test both.