Not particularly an automatic fan myself, but my truck has a 4L80, and it shifts beautifully. The programming is superb from the factory. And with a 3.73 rear, it still cruises nicely at 70-75. Course it's behind a 6.2 diesel, and was a military issued GMT-400 stakebed, but the possibilities do exist. Just need to get past the bell-housing.
A buddy of mine had a ("cough cough") Camaro drag car, and broke quite a few bellhousings before getting his problem squared away. Altho the problem was alignment, (not the bell), he opted for one of those "Super-Bells". If you know anything about them, you cut off your original from the case, and the aftermarket housing bolts to the frt pump. (not a fan of that either), but he didn't have any problems. Then again, he didn't use it very long, B4 he spent mega bucks on a race P/G. (Gross).
Point of the story, wonder if there's a "Super Bell" with a Poncho pattern, to a 4L80 tranny? (I seriously doubt it)