I've now tilted the seat up a little, and, after three rides, I'd say it's better - not perfect, but better. But I still can't just forget about it - still have to keep changing my position, standing, etc, to avoid tingling. And I don't mean every once in a while - I mean I need to change my position every minute or so, and stand up to let the pins-and-needles subside every couple of minutes. I was figuring that this just goes with the territory of being 60-70 lbs heavier than I was when I used to ride a lot more. Now, I'm wondering if that's true.

I think I'd like to try your solution. Did you approach it in gradual stages? I set the height of the saddle using the method of putting my heel on the pedal at the 6 o'clock position, and setting the height such that my leg was almost straight, but not locked. (This is what I was taught.) As far as the fore-aft position of the saddle, I always just sort of eyeballed KOPS, with me sitting in the saddle and looking straight down over my knee at the pedal (never really used a plumb-bob). Did you depart significantly from these guidelines?

I've been considering something like a Selle-Anatomica saddle, but before trying a gear-oriented fix, I'd like to experiment with making some adjustments to what I have.