There's an instrument cluster diagnostic built in to these clusters that may be helpful. I forget the exact procedure but basically just involves hitting the trip odometer button - search here or Google for instructions on how to activate and use the diagnostic feature.
Anyway, it will display various analog cluster readings (rpm, speedo etc) in the odometer display. It would be helpful to know if the cluster is getting a speed signal from the pcm, and this test should clarify that. If you get a speedo reading in the display then there is likely fault with the cluster, such as a bad stepper motor.
Something else that may be worth trying is swapping the original cluster back in, see if anything's different.
Anyway, it will display various analog cluster readings (rpm, speedo etc) in the odometer display. It would be helpful to know if the cluster is getting a speed signal from the pcm, and this test should clarify that. If you get a speedo reading in the display then there is likely fault with the cluster, such as a bad stepper motor.
Something else that may be worth trying is swapping the original cluster back in, see if anything's different.