I just bought a suburban 99 k1500 4wd gas 350
on the way back from purchasing from a guy on Facebook marketplace it threw a p0300 code. I have put in New plugs and wires and a new coil pack .. And a new secondary o2 sensor because one time after clearing it it threw that code with it.... Checked for vaccume leaks just visually just going down the list. Any suggestions or tips would be helpful.

 

My old '99 Yukon 5.7 had the plastic housing distributor in it go bad at 90k miles. It was causing random misfires under load.