What they're all trying to say is that very likely the problem is the tach sensor, and possibly the wires or connections for the teach sensor. You know that the tach sensor is mounted on the IP gear tower, with about a 1 inch head shaped for a wrench. It has 2 wires coming out of the top. Those wires may be frayed, but more likely the sensor has gone bad.
If you disconnect the wires for the sensor, and unscrew it, pull it out, you may find that it's dirty. Clean it off and put it back in. If it works now works, consider that a temporary fix. It's probably on it's way out, so start preparing for a new one from the dealer.
Yes, the tach sensor feeds the TCM, transmission control modual, as does the VSS on the rear differential. If either of these sensors becomes erratic the transmission will go into limp mode, shift hard.