Is my compressor shot?

Steve do you have a clamp on ammeter? If you do try measuring draw soon after starting cold, then if you can get it to trip measure it as soon as you can close to it tripping/ warm. Immediately pull the belt and "compare by hand" rotate the compressor by hand and judge if it is any tighter to turn than cold

The compressor likely will not seem to have compression by hand......the unloader should be released if the pressure switch is open

The "scrubbing" you felt when rotating the motor could well be the start switch...so normal

A start cap should not cause tripping when running. Start cap only in circuit when starting,as soon as the start switch "flips" the start cap is disconnected. If the start switch sticks, it will pop the breaker on startup and make lots of grunting and noise from over-current

The run cap is a different matter.