OBD codes 0708 & 0700?

[chessy56]

2001 Silverado, LB7 D-max w/250K miles:
SES indicator regularly lights. Truck goes into limp mode when shifting to Drive. Shift to park and shut off engine and immediately restart- no limp mode. (Sometimes it takes a second re-start before limp mode clears). This has been happening for the past 6-8 weeks now.
NSBU was replaced for the first time in 2008, again in April of 2011 (after gear indicators on the cluster started appearing flaky) and once more in September of 2011. A local auto supply store pulled codes 0708 and 0700 from the OBDII port. Is this an indication of yet another switch or do I have something else going on? One posting on an internet site suggests the ignition switch has something to contribute to this as well. (Really?)
Does this have anything to do with any of the 3 solenoids located inside the T1000 Allison? Can anyone help on this? Would like to get this resolved before the snow flies.....

[chessy56]

Anyone with experience on these codes???

[More Power]

Having so much trouble with the NSBU could indicate something related to the NSBU might be a contributing factor - like a wiring/connector issue or improper installation. The NSBU must be properly indexed to the Allison gear selection shaft during installation. A new NSBU should come equipped with a removable metal lock that positions the switch shaft in the proper location, and the Allison gear selector must be shifted into the correct position during switch installation. This metal lock is removed immediately before being pushed onto the Allison gear selector shaft - only after both the NSBU switch and the Allison gear selector shaft are in a matching position.

For each of these trouble codes, the Malfunction Indicator Lamp (MIL) will illuminate when the diagnostic runs and fails the first time. In addition to storing the trouble code, the operating conditions are also recorded in the "Freeze-Frame" records.

P0700 - MIL Illumination Requested - P0700 is set by the vehicle ECM, indicating that the TCM is requesting MIL illumination. This is the most generic of all the Allison codes. For example, this code will set if the Allison is low on fluid or if it slips during a high power launch. Generally, another, more specific code will also set - though not always.

P0708 - Transmission Range Circuit High Input - This DTC can be, though is not necessarily, NSBU related. The TCM has detected an invalid condition along with parity errors over more than one consecutive ignition cycle.

Jim