Inspect your ring gear on the flywheel for damaged teeth, if it looks good your starter solenoid is not throwing the gear out to properly engage with the ring gear. The starter has 2 sections, a solenoid which pushes the gear out and the main motor which rotates the gear after it has been pushed out and engaged with the ring gear. Just because Kragen said it works does not always mean it's true. Some things are hard to test properly on the bench.