Ok, I watched the other program that was recorded the same night. No dropouts. Here's the score:
Lost (7:59-9:00, local ABC, tuner 2): No dropouts (amazing!)
Simple Life (8:30-9:03, local FOX, tuner 1): No dropouts (Wow!)
American Idol (9:00-10:03, local FOX, tuner 2): 1.67 gazillion dropouts (ouch)
So I guess it's fair to say in my case, that it was neither specific to that channel, nor the tuner. I don't know what the heck was going on. I wish I could remember if we were playing back another recording at the time.
I rechecked the signal strengths on both tuners, both sats (110 & 119). The lowest signal strength I got was 86. Most were mid-90's and a few over 100.