Detonation on 2001 GMC Yukon XL Denali

I seem to be experiencing a lot of detonation under minor accelleration both around town and on the highway. I also have the piston slap at startup, but the noise on the road sounds more like detonation. I've tried high-octane gas, but that hasn't helped. My truck has 190,000 miles on it, and has been well cared for all of those miles. Any ideas on decreasing the detonation?

by in Hopkins, MN on July 10, 2010
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