?Isn't truck is a "platinum 2" series, that has push buttons on sides the dash? if so, there are other instructions on how to clear the codes.
Some day, Raytech will get his round tuit out, and add his e-mail to his profile. (or maybe just send me an e-mail and let me know that e-mail came from "Raytech")
I could be very wrong about this but in my experience, on these trucks the -ECM-' (E codes) "limp home" modes were all about engine cutback speeds, and the only things that cut out the transmission were related to Can bus errors or the transmission itself. I am guessing at this point that your problem is actually in the dash, where one of the can bus' "termination" resistors is located (the schematic makes it look like the resistors are in the ECM and VCM, but trust me, one is in the dash) is there any chance that you try the dash from a known good sister truck? the dash can be swapped with no "learn in", as a test. most times the error is that the vcm and ecm are not communicating as the dash can bus 'Knock Out' error, but I would bet an intermittent connection to either the can bus on the dash , or the resistor itself might cause this KO on the can bus, at least in the platinum 1 series it was..
I would be willing to bet that if your scanner had a setting for a Nissan Sentra of about 1999 model year, it may be able to clear codes, but if your OBD2 scanner requires special cards or modules to access those vehicles, you would need that module/card.