Ready to go racing after 15 months off!

Made 4 passes Friday night. Car has weird issue. Runs good 1 pass then pops and slows way down the next. Then it's good again, etc.
I'm thinking maybe the crank sensor. going to try replacing it with a spare I have and see if that makes any difference. Problem is I don't run a modern ECU that would store a code if the sensor was bad, so it's a guessing game.