Is it a 9C1 or a civi? Are running an L03 or L05 motor? The second question isn't as important, but having owned 3 9C1's, there can be a lot at work you don't realize.

I second the wiring check, especially your ground straps. Shifting into park (next time shift into neutral instead) just takes load off the motor allowing it to correct itself normally. Check your battery cables and ground as well.

I've got a T56'd '96SS and my wife drives a T56'd '94 Caprice Wagon, so I know "a little" about these cars. My first B-body was a '93 OSP 9C1.

__________________
-James

'85 280GE...sold
'96 Impala SS ~ 6-speed 396
'14 Cadillac Vagon. . . . . . . . . . "Life without knowledge is death in disguise." - Hans-Peter Geerdes