2003 S type R 87K miles.
When on Freeway some times my girl does the following.
Speed around 100kph(60mph) increase acceleration slightly this is not a WOT, engine "howls" like a dingo (wolf) a very quiet howl almost muffled, engine accelerates a little then kicks down, revs jump, and "gearbox error" pops up on display. The gearbox appears to lock into 3rd gear.No other lights.
Stop car, turn of ignition, immediatly turn on ignition. fault has cleared, start engine and proceed as normal.
I purchased an OBDII reader but it will not read the codes, maybe I got the wrong one!
Got me stumped!, I have read evry TSB evry hint, every clue or thread that has gearbox error in it, running out of ideas HELP!

 

Bear in mind there isn't a TSB for every fault. That's not what they're for.

Could well "just" be low fluid.

Maybe S307-15v2 Transmission Noise During Gearshifts.

Maybe S307-11 AUTOMATIC TRANSMISSION - GROWLING NOISE IN FOURTH GEAR DURING WARM-UP (doesn't mention STR but it likely does apply).

I don't think either of those 2 cause a gearbox error, though.

Or maybe a TC (torque converter) problem.

 

...it's most likely your torque converter. There is a TSB for early STR tc issues. What you are experiencing is exactly what I went through before rebuilding and replacing my tc.

This advice is worth exactly what ya paid for it...