pm26

Better quality interior? With plastic tool shed wall door panels and cheapest looking lint collecting seats imaginable? Don't make me laugh. And if coil over strut suspension is so strong, why did they retain front torsion bar suspension on 2500 and 3500 series trucks?

HaHa! I can honestly say I've never heard that one before. Well, GM did eliminate some nice features that LT GMT 800 trucks had as standard equipment. Decent bumpers, body color fender flares, rear window defroster, automatic dimming rear view mirror, torsion bar front suspension on the 1500 4WD models, and much better quality inner door panels and cloth seats. On the other hand GMT 900 trucks benefited from the new front suspension to give them a car like ride, and the dash has been lowered for better view of the road . Also, the new 6 speed auto transmission is a big improvement. However, addition of the AFM system on the 5.3 liter engine negated the upgrades in my opinion.

You may have a defective knock sensor. What it may be doing is advancing ignition timing too far and then pulling back when audible knock occurs. Honda Odyssey vans had this problem several years ago. I was reading a number of complaints where the engines would knock regardless of the fuel used. Just a thought. With a good knock sensor, even if you ran regular 87 octane in your engine, there should be no knock as the knock sensor should cause the ignition timing to retard somewhat, thus eliminating the knock. You would experience just slightly lower performance, that's all. I do not know what kind of noise you are experiencing. What I described above would be engine pinging. As Stealth pointed out in the post above, it could be a leaky exhaust gasket. i had those on my Nissan pickup at about 90k miles (their 3.0 liter V6s were famous for that) and there was this rumbling noise on acceleration until the engine got hot, then the noise stopped, because the gaskets expanded and sealed better.