The TPS was often the cause of codes like P0731/P0732/P0733. It's not hard to replace, however, proper adjustment of it is critical and the closed throttle position must be relearned afterwards. As far as adjustment, the procedure is specific and requires using feeler gauges and an ohmmeter. Consult the TSP or the EC section of the Factory Service Manual for the proper procedure. Relearning the closed throttle position technically requires a scan too to monitor the switch to see it switching from "on" to "off" while turning and releasing the throttle drum. Usually, turning the key "on," then turning the key "off" after a couple of seconds and repeating this cycle about 12 or 13 times will work. That said, a faulty TPS will not cause a no reverse situation. You already stated the shift cable was good. The most likely cause is a bad reverse clutch drum. What often happens is the snap ring will pop out of the groove in the reverse clutch drum which makes it impossible for the piston in the drum to compress the clutch frictions and steels together. This occurs on a number of automatic transmissions, not just Nissans. It use to happen a lot in the Chrysler transaxles used in the 90s. The fix for this, however, is teardown the transmission and replace the reverse clutch drum (at which point, one might as well rebuild the transmission) or replacement of the transmission.
