I can already see more improvement. I filed up with 22 gallons of B20 last night, which was mixed with the remaining 7 gallons of ~5% bioD and whatever gunk was sloshing around underneath my pickup tube in the tank. I also went ahead and gave the tank another 8oz shot of Stanadyne performance Formula to help tie up whatever water was still in the tank (if any).

By the time I had driven the 9 miles back to the house, she was running as "smooth as warmed butter" again at low speeds and slow acceleration rates. This morning, I didn't notice a single episode of the surging and lunging I had been experiencing, and the motor settled into her quiet rhythms a lot faster than she normally does, and that is even with ambient temps beginning to drop a little (high 50's and low 60's at night).

Sooo.... I am now planning to make my two back-to-back 200 mile day trips today and tomorrow (which will include another fill-up with B20), and see how the fuel pressure gauge is reading on Friday afternoon. If she's bouncing around again below 60 psi, then I'll make one more change on both filters and just plan on shooting straight ahead. If I continue to feel periodic stumbling and surging at low speeds after these trips, then I'm going to drop the tank and clean it out this Saturday, but I really am not expecting to need to go that far right now.

On a side note, I talked with the the guy at the station last night, and he said that they are making their own bioD and then mixing the B20 blend themselves, which means that they are not buying from the "market" and should have more control over quality. He also said that they fill up their tank about once/week.

I appreciate you guys' input and sharing your experiences... you're a great encouragement.