My Vette makes a pinging/knocking sound when I accelerate hard - especially in the summer with the A/C on.  I had a lot of work done to it and asked the mechanic to replace the oxygen and knock sensors.  They didn't because they said they checked out fine when hooked up to the computer.  (I use good gas, highest octane I can.)

Any comments or suggestions? 

Even with the timing dead on you may get knocking on hard acceleration with todays methanol/gas mixtures that are sold almost universal now.  I have the best luck with Mobil Premium here.  From what I have seen and heard, a light knock is not a major issue, severe knocking can be devastating.  Knock sensors are a separate animal.  They can give incorrect feedback to the electronic timing if they are tightened too much or too little into the block. 

Check your EGR system, make sure its not pluged and all the hoses  that controll  it are hooked up and in good shape. Low grade fuel, to much timing, over heating or lean mixture can all cause this problem. Good luck!!

silly question but are you running premium in the car? makes a huge difference....in the '88 owners manual it states premium fuel recommended.....not sure if previous owner didn't care, didn't know or whatever but after 2nd tank of sunoco 93...it ran MUCH better and stopped knocking on acceleration....

+1 on the EGR. And, as already stated, minor knock isn't an issue....these engine can take quite a bit of that, nut excessive, continuous knocking/pinging is damaging, and needs to be corrected. You said you used the best fuel you can get, so that's good. I wonder how they checked the knock sensor? If it is not responding, or not responding quickly enough, it can certainly cause excessive ping.
Over advanced timing can do it, too, as can engine temps that are too high. A vacuum leak can cause a lean mixture, and create a ping.
So many possibilities....

Yes, I stated I ran good gas, highest octane I can.


Thanks to all for tha suggestions.  I'll print your comments out and start checking the items you mentioned.

RitaJean, is your '95 throwing any codes?

No.  I'm seeing no codes on the dash info center and none are showing up on my mechanics computer.  All items like the ERG valve, the O2 sensors, knock sensors show they are working okay. 
I've had it "scoped" at my mechanics and according to the computer there is nothing wrong with the car.
Just causally moving down the road, no A/C, under no load, it runs - just okay.  Especially in the early morning (I leave for work at 4 AM).  And in the winter/fall months it isn't as bad.
But when I drive it like a Corvette, especially a hard acceleration - like getting on the freeway - with the a/c on it pings and knocks.  I live in Arizona and the hotter it gets the more noise it will make.
The frustrating thing is my mechanic says he can't find any thing wrong and is of the mindset he won't replace any parts that he can't determine there's a problem with.  So, I'm thinking of tearing into it myself.  I have done some work on it, I'm fairly mechanically inclined, I just need the advise of my C4 registry guys to make sure I'm headed in the right direction.

Well good on your mechanic for not changing parts for nothing.  But, besides checking codes and scoping the engine did he do anything else?