Hey guys. Having a little problem with my suburban. Its running really strong but I have noticed under a light load it sounds like its pinging. I noticed it mainly when its locked up in 4th. It sounded worse when I was pulling a trailer with it (in 3rd of course). It really sounds like spark knock. I'm using 87-octane. Thought that would be plenty. I dont really know where to start in this thing. Since I got it I've replace fuel filter, plugs, rotor & cap. Its strange cause the CEL does come on and throws code 43(rough running if I remember) but it only does that if I cruize for a while. Under acceleration it doesnt ping or anything. Also I notice it really bad when I cruizing in 4th, locked up and I ease into the throttle trying to get it to downshift. Just before it kicks down you can hear it ping really bad. Then when it downshifts it doesnt do it. Anyone got any ideas? I dont really know how these systems work otherwise I could probably just diagnose it myself.