I'd agree that it's most likely ****ty or disconnected grounds.
That being said, I think your starter has a different issue. The only time I've had poor starting speed is:
1) bad batteries
2) bad starter
3) not good enough current running to the motor. Make sure you run some decent 0 awg line from your starter to your battery, jump the ground from the relay to the starter ground (neg), and make sure your positive line from the relay is getting a full 12V when you hit the ignition (easy to test with a multimeter).
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Corey - BSME '21 Tesla Model 3 Perf
'22 DMax AT4 2500
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