Hard shifts on 3.8l w/ 4T60-E Transmission

'96 3.8 w/ 4T60-E transmission w/ 70k miles since new suddenly started shifting hard (abruptly) on all upshifts. Downshifts may be a tad hard as well, though to be honest, we've driven the car so gently I doubt we ever really forced downshifts before.

All shifts are at the appropriate time, and the TC appears to locking/unlocking properly.

Dropped the pan and noticed one of the steel lines (the one rear w/ a bend in it and having a rubber hose in it) disconnected from the valve body. Re-attached (thinking I'd found the problem), replaced filter and fluid, but there was no change to quality of the shifts.

The pan was very clean (no debris or sludge), but there was one thin (maybe 0.025" thick) piece of broken metal (about 1/8" X 1/4") with a curve to it that could be part of the edge of a clutch plate/disc stuck to the magnet.

Problem kind of started after an intake manifold backfire on one start that
blew the line off the throttle body that goes to the fuel pressure regulator and the vacuum solenoid on the front of the transmission. What is this vacuum diaphram device for, BTW?

Ideas or suggestions?

Thanks,
Bob
Waxahachie, TX

What model GM car is this?

The part is a vacuum modulator. The 4T60E autotransaxle uses a vacuum modulator controlled by engine vacuum to control line pressure. If bad it will affect upshifting or give hard shifts. The metal pieces found doesn't sound too good.

I've got a question? What is considered a hard up shift?