Starter Stays Engaged... Please Help

[TN4X4]

Could use a little advise since I'm new to the classic Chevy world. I've got a '72 K20 with a baseline 350. I've just replaced the starter and solenoid cause it sounded like it was dying of heat soak. Now the new starter won't shut off. I've read a similar post on here that covers this issue and the solution seemed to be shims because the gears are too tight. I've put what looks to be about an eighth of an inch of shims on the starter and it still won't disengage. I've traced the purple wire from the igntion to the "S" post on the solenoid too. It appeared to be fine. I'm at a loss on this one? Should I shim it somemore? Thanks.