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Transmission will only shift first two gears.  And also will not move in reverse until engine revs to 2000rpm.  Trouble came on all at once, no prior trouble, no slipping.  No warning lights come on.  fluid looks very clean and smells clean.  

Did you ,or do you have any way to pull the codes from the EEC (PCM)? Or even do a pressure test for reverse? It really could be any one or a combination of sensors,or quite possible internal damage.

Shift solenoids A and B provide gear selection of first through fourth gears by
controlling the pressure to the shift valves.
PSOM receives input from the rear brake anti-lock sensor. After processing the signal, the PSOM relays it to the powertrain control module (PCM) and the speed control module.TSS Sensor is a magnetic pickup that sends the powertrain control module (PCM) information on the rotation speed of the coast clutch drum. The PCM uses the TSS sensor signals to help determine EPC pressure, shift scheduling .
OSS sensor is a magnetic pickup that provides transmission output shaft rotation speed information to the powertrain control module . "The PCM uses the OSS sensor signal to help determine electronic pressure control pressure, shift scheduling and TCC operation.  The DTR sensor completes the start circuit in PARK and NEUTRAL, the back-up lamp circuit in REVERSE an a neutral sense circuit for GEM control of 4x4 low engagement. The sensor also opens/closes a set of four switches that are monitored by the powertrain control module (PCM) to determine the position of the manual lever.  

How many miles on it?If you get no codes you could drive it with a scanner in data mode and see if the computer is commanding the shift and also drop the pan and see if there is any clutch material in there.