Yup, you need to keep at the tuning.

Pay particular attention to performing the pinch tests at high and low throttle.

Also do all tuning with only 1/3 of a tank of fuel. This is rather important.

Finally don't forget the 60 second nose up test, and the 60 second nose down test.

Once you have all of these dialed in, the engine will be very reliable.

Like most non OS engines, the Magnums just need a bit more TLC to get the tuning right initially, but once set they run very well.