Question

2003 Chevrolet Tahoe 5.3L with engine code P0300, cylinders 2,4,6,8 only. I did a catalyst backpressure test at idle: 0.0 & 2500 0.0
Swapped HO2 sensors position the one on the left and right bank. No lean code is stored.

Answer 1

P0300 Random misfire

Do a compression test, you would need to rule out a mechanical condition.

Answer 2

P0300 Chevrolet Code - Engine Misfire Detected
Read more: https://www.autocodes.com/p0300_chevrolet.html