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2002 Bonneville SE 3800 NA 200,000 miles. My knock count(22125e) is always 1, even during KOEO. My KR goes up to 5 and my rpm is below 2200 rpm. Sometime kr is 0 on the highway. My fuel trims are under +- 5, ltft +stft. In the last year I have changed plugs(xp606), maf(denso), map(ac delco), fuel injectors(rebuilt), fuel filter, fuel pump(ac delco), front left trans mount, both front wheel hubs, both o2 (ac delco), valve cover gaskets. Replaced defective egr valve. Also did a compression test which came out good. My mpg is low,24 mpg 70% highway. Tested for exhaust leak, none. Torque pro shows no problem with trans shifts and zero slip. Tested my tps and was linear. I think my kr is non zero too often under light throttle <20%, knock count always 1 and my mpg is low. I noticed my mpg increases to over 30 when kr is zero on the highway crusing. Could it be other mounts? My mpg dropped 1.5 years ago from 30 to 24 and have been chasing the cause. Any suggestions to get my mpg up would be appreciated.

24 mpg is not low for 70% highway. What speeds are you driving? Remember that we are also on winter blend fuel right now which takes fuel economy down a few notches, as does the temperature.

With a stock tune, the L36 will have knock pretty much any time there is significant load.

I was averaging 30 a year and a half ago. And the lower mpg has happened through all the seasons. I drive at 72-75 mph.

Did you change plug wires?
Also I may be wrong but I vaguely remember GM saying changing EGR needs a CASE learn to initially set new one.

Plug wires are 3 years old. I did do an ohms test recently and they all tested good. The new egr seems to respond linearly between duty cycle and egr volts. The other thing I did was run the engine in park to 3500 rpm. No kr in park. I also filled the tank with 16 gallons of 93 octane. Drove for over 200 miles and the kr was behaving just like when I have regular gas, I am naturally aspirated.