The starter does one simple thing. It spins and makes gear to gear contact with the flywheel thus turning the engine fast enough for it to start. The only sure way to test a starter is to remove it and have it bench tested at an auto parts store.
Remove the starter and have it bench tested.
It may be possible that the wire connections on the starter or battery are broken or corroded. It could be your starter relay. Or your starter should be tested to see if it needs replaced.
check for power to starter; check fusable links at positive battery connection, can you jump starter directly with power source? if not maybe the starter should be taken out and inspected/bench tested. given the year I suspect wiring/connection issues. a worn out ignition switch would be common for this age of vehicle. check operation of starter relay. check for power to starter; check fusable links at positive battery connection, can you jump starter directly with power source? if not maybe the starter should be taken out and inspected/bench tested. given the year I suspect wiring/connection issues. a worn out ignition switch would be common for this age of vehicle. check operation of starter relay. check for power to starter; check fusable links at positive battery connection, can you jump starter directly with power source? if not maybe the starter should be taken out and inspected/bench tested. given the year I suspect wiring/connection issues. a worn out ignition switch would be common for this age of vehicle. check operation of starter relay. check for power to starter; check fusable links at positive battery connection, can you jump starter directly with power source? if not maybe the starter should be taken out and inspected/bench tested. given the year I suspect wiring/connection issues. a worn out ignition switch would be common for this age of vehicle. check operation of starter relay. check for power to starter; check fusable links at positive battery connection, can you jump starter directly with power source? if not maybe the starter should be taken out and inspected/bench tested. given the year I suspect wiring/connection issues. a worn out ignition switch would be common for this age of vehicle. check operation of starter relay.
If 12 volts is being applied to the starter and it will not function, then remove the starter and have it tested at an Auto Parts Store.
Remove the starter and have it bench tested at your local auto parts store.
Remove starter and have it tested for drag, load and shorts
The starter solenoid may be bad. On a Chevrolet, it's integrated with the starter so you will have to remove the entire assembly (should be 2 9/16" bolts going up and unhook the 3 wires going to the starter, then take it to any auto store and get it tested and if necessary replaced.
See link.
Have the battery and/or starter tested for free at your local auto parts store.
Remove it and have it bench tested.
No animal should ever be tested on
Since you changed your battery and starter I'm assuming you are getting fuel and spark is your problem. You should check your starter relay, the wires from the relay to your starter, the wires from your battery to the relay, the wires from your locking cylinder to the relay, and your locking cylinder. You might also check your alternator. You can take it to a parts store to have it bench tested for free.