I talked to a local CIH mechanic this morning.  He seemed to think it was likely a bunch of corn leaves stuck in the cold air intake or small cracks in the fuel hose going from the tank to the lift pump letting air into the system.  I took the cold air intake off and looked at it again.  It was still clean.  The fuel line going to the lift pump looked to be in good shape, but I replaced it with new hose anyway.  Then I went to the field for the day, and it was still acting up.  I checked for more responses on this thread and noticed the possibility of the air intake hose from the filter to the turbo
collapsing.  I tilted the hood forward and ran wide open across the field pulling a little over 8 mph with my face against the windshield to watch the air hose going to the turbo.  about 1000 feet later it happened, and I thought there was some movement on that air hose.  I adjusted my position again to get a better view and tried it again.  This time the hose could clearly be seen collapsing.  Normally I would have associated such an abrupt loss of power with a fuel issue since something like a plugged air filter happens more slowly, but this hose collapsing happened in the blink of an eye.  Not only that, but the hose also instantly regained its normal shape as soon as the engine lost RPMs.   Being only inches from the turbo, the effects were nearly as immediate as a fuel issue could be.  The possibility of that hose collapsing never would have otherwise occurred to me. 

I called the parts guy at the local dealership.  He is one of the best parts guys I've ever seen.  If the wild west movies were made of parts guys instead of gunslingers, this guy would been the fastest draw in the west (I say this based on years of experience with him quickly getting the right part when others would take a long time to get the wrong part). He said there were only two of those intake hoses in the country at two dealerships.  He called the closest one and will have the intake hose here for me tomorrow. 

Thanks to all of you for your help in solving this mystery.  I'd offer all of you a beer if you were here.  Since you are not here and I am, I'm drinking this beer now in your honor and heading off for a little sleep.  Thanks again!