Knock Retard question

[krazy86t]

My car develops timing retard with 10-15psi boost on warmer days once the engine is warmed-up. Also seems to be related to throttle application. I get more KR with gradual throttle application building boost >10psi vs. off the line and WOT. Off the line WOT is fine - AF hits 255 pretty fast and no KR. Gradual throttle slowly gets to 10-15 psi, but AF is 150-200 and O2 voltage is about 800 and dropping to 740-750. stock MAF is replaced with LT1 3", TT 91 octane chip with 42lb injectors.