From what you're saying, Bill () is that the ECM is seeing the proper signal, so the signal is ok. You also said the pink wire and grounds are OK. Whats left is the gauge cluster itself.
The needles aren't cable driven like the old days where a bouncing speedo or tach is just a mechanical fix. The needles are attached to stepper motors and they will do nothing if they lose power, not drop to 0. They would stay in place. Which leads me to believe (using your info) that you should remove the gauge cluster, carefully check that connector at the pink wire pin, and trace that on the SMC board to the stepper. Look for bad solder joints because it sounds like a temp driven loose connection.