Hoping someone else can chime in, b/c I don't understand why caching would do this. All major online publisher (I even work for one) use page caching I assume, I doubt they would let this affect their ad impressions served.
Based on my Pingdom tools link, can the issue be that my site now loads very fast and the ad tags are loading towards the end so many users are already on the next page before the ads have had time to load?
Thanks again!