Gene, I'm really sorry to hear that we haven't been able to get this problem behind you. Assuming that you have the connector of the new tach fully snapped into place, then the primary likelihood is that your new tach is bad
Locally, "we" (that means Ryan) just replaced a tach for a local customer and all was great. The new tach was straight from Ford inventory.
I've said it before - perhaps even in this thread, but I think the following process should ALWAYS be followed when starting these cars.
1. Key to full "on" position
2. WAIT until odometer display appears
3. Press START button to fire engine.
The WAIT in step 2. allows enough time for the gauge control module to sync with all of the gauges.
Gene, I wish I had something better to tell you, but I think your new tach was DOA (dead on arrival) and assuming you got it through Ford, they should exchange it for you.