Detonation/Pinging

I have a 2000 with 4.3l v6 5spd. Can someone help me out with a list of all components to check to find the cause of my detonation/pinging problem? I've changed the dist cap and rotor, fuel filter, spark plugs, oil and filter, air filter, knock sensor. I've tried 89, 91 and 93 octane. The pinging is reduced as the grade of gasoline increases. As a matter of fact it pretty much disappears with 93. However, at 93 octane I seemed to lose power. Is that possible? Also, at nearly $2.50 a gallon it's getting expensive and I'd rather try to fix the problem. This has been going on for over a year since I bought it. There is a definite coolant smell coming from under the hood and i can see a drip at the botom of the oil pan. It never leaves a puddle. Does not seem to be producing steam from the tailpipe. Temp guage is constant at around 195.
Thanks.

You shouldnt be losing power with higher octane that makes no sense really the higer the octane the better the burn completion and combustion. Very weird though!!! I think you need to lay off the lowoctane gas for a while have you always used low octane or did you just start when gas went up??? If so then dont short cut it just use the expensive stuff for now cause what you lose in expense now you'll definatley save in maitanance later trust me on that one!!!!But if you've always used the same octane though then you should check your pcv valve and see how much oil is in it and if theres a significant amount then change it and reclean out your intake manifold(Dont use easy sprays to clean it either!!!)

you can try some combustion chamber cleaner you may have excessive carbon buildup.
also run a tank of high tes and some fuel system cleaner to clean out out the injectors.
if this does not clear it up you can check the egr valve for carbon buildup on the valve.
as for the coolant leak you need to take a good look to see where it is comming from, check the bottom of the waterpump (most likly)

Thanks for the responses. I'll give these last few things a try. The whole octane thing is really wierd. For a while I was running 89 and didn't ping for a while. It was also colder out. The 89 eventually started pinging so I bumped up to 91. 91 also stopped the ping but is harder to come by than 93. I was using 87 for at least the first 8 months of owning it. Never thought to listen for ping the first several months so it's hard to tell if it was always there. I guess my overarching concern is if the 93 octane stops the ping, is there still a hidden problem that will come back? I guess for the amount of time I plan on keeping the truck running 93 is certainly cheaper than replacing things or bringing it into the shop every few months.