Ethanol is actually an excellent octane booster. I doubt it causes your pinging.
Again I repeat, pinging is most often caused by running lean. Check your Long Term Fuel Trim. This value requires a scanner to read. It will tell how much the computer has to adjust the mixture off factory values. If the LTFT is not within ± 5%, ideally with ± 3%, then you have a fuel management problem. Positive values means the computer is detecting a lean condition and attempting to add fuel to compensate. Possible causes include: vacuum leaks, intake leaks, dirty or defective MAF sensor, fouled oxygen sensors, misfires, incomplete combustion, faulty PCV valve, etc.
These vehicles are old enough that the vacuum lines can deteriorate. They are also old enough that the intake manifold gaskets, both upper and lower, can shrink and crack, also introducing leaks. This is very common, possibly the most common cause for pinging. There are test to check for leaks, but in order to perform them accurately, you need a scantool. A better approach is to simply check the condition of the hoses, especially around elbows. The PCV elbow is a common leak site.
Another common problem area is incorrect ignition components. All to often people think that because they have replaced the spark plugs that they are good and that the new plugs could not be part of the problem. These engines are very picky about the quality of the ignition components. The only brands that work well in these trucks are Motorcraft, Autolite, and in some cases, NGK. They have to be the correct gap and heat range, they must be double platinum or better, and they must have a single tip and electrode. Parts from other brands often create pinging because the heat range and displacement of the plugs is wrong, or parts of the plugs get too hot.
The MAF sensor can read incorrectly if it gets crud on the element. This can happen to any MAF, but is more likely to happen if you are using certain kinds of air filters, namely oiled filter elements. They are also more likely to get contaminated if you do not replace the air filter on a regular basis. There are specialized cleaners that you can try spraying on the element to see if that doesn't help. The MAF can be tested as well, not sure on the procedure.
It is possible that carbon deposits can have formed over time, increasing the compression ratio, and that can result in pinging. Various tuneup shops offer services to clean these deposits from your engine. In my opinion, these are worth the investment. A cleaner motor performs better. It is not recommended to use an octane higher than the one recommended in your owners manual. If you do so, it can contribute to carbon deposits which can cause pinging, not prevent it.
Ethanol is not going to cause pinging in the short term, E85 has a rating of 105 due to the high ethanol content. E10 is rated at whatever the pump states, but the ethanol itself is a high octane fuel. Its also very good at cleaning the motor and removing deposits. Don't get me wrong, I am not a fan of ethanol, I'm just stating that your assessment of it is incorrect. For the record, Virginia and North Carolina both have Ethanol gas unless the pump specifically states otherwise. Your lack of pinging in those areas could have to do with a long drive cycle or an elevation change.
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