I know. It's driving me crazy. I just checked the vacuum with a gauge and it is steady at 22 which is normal. I thought maybe a clogged cat. but the vacuum was steady during acceleration all in normal range. I'm going to get the temp. before and after the cat with an infrared thermometer and see if there's a difference. I know that would be an expensive fix but at this point it would be worth it to get this headache over with.
Hate to say it because it's been such a good truck, but I'm to the point where it's not really worth spending any more money on this problem, not with 373,000+ miles on her. Unless you or anyone else finds an easy fix. And I think we've exhausted the easy fix options.