I have a problem with my workhorse engine. It's a 2000 model 454 with fuel injection. A noise, the closest description would be a valve ping, that developes in lower gears under load. This started at about 3000 miles. I have had it in several times both in and out of warranty. They have changed fuel filters, plug wires, dist cap. The plug wires seemed to soften the noise a little and high test gas helps some but 42,000 miles and it's still there. Would appreciate and suggestions?