Buick 4T60E trans lock-up problems

I have a '96 Buick Regal 3.8 with 180k miles. I've changed the tranny fluid/filter several times in its life but since this last change I seem to have a problem. The trans will shift normally during
acceleration hot or cold, light or heavy pedal but once the lock-up is engaged it will unlock and relock with a slight push on the pedal. When I say slight, I mean, for instance, the slight fluctuations of my foot when hitting a moderate bump in the road will cause it to unlock/relock. Other nuances: a very slow and steady pushing on the gas will not cause the problem.....a decent push on the gas at the base of a hill will cause it to unlock but it will stay unlocked appropriately for the load going up the hill....it will do the same thing in overdrive or '3'. I have a tach so I can see exactly when the unlock/relock occurs. Sometimes I get a shudder when the trans seems to be unsure whether to relock or not.
When I was changing the fluid I wiped off the gasket surface and the rag caught on a piece of metal about 1/4" wide 3" long with a 'V' bend in the middle and knocked it off. This was up next to the filter. I put it back on the way it made sense i.e. with the 'v' pointing up holding another piece of metal in place against the valve body (maybe, I can't picture it in my head now).
Any suggestions as to what might be causing this odd behavior? And did I put that thing back on right?
Ron
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