gq overdrive problem

120 thou??? where's it been all this time?
what do you mean shutters? Do you mean Shudders by any chance?
Diesel or petrol?

I had a similar problem with mine (Diesel - Auto).

Several "EXPERTS" told me it was the Torque Converter.... Quotes from $800-4000 for rebuild.

Took it to KB Auto in Berwich, (that AWILL4x4 put me onto) and told them to fix it.

Dave from there called me back later in the day stating it was only an adjustment on the Diesel Pump, as to when it changed Gears, in this case, into Overdrive. It was changing at too low revs, and shaking the hell out of the car. he could have done the rebuild, and charged me $900, but gave it a service, and adjustment, $200 I was on the way home... BRILLIANT SERVICE...

Its a screw and slotted plate, you losen the screws, and then turn it one way or the other (trial and error) if I remember, but get it looked at. Autos are expensive as hell to rebuild. Although it could be hard to find someone who wont shaft you, but they are out there. But I do Highly recommend KB Autos.

I have a 1990 GQ Patrol auto. Lately (about six months) it has been apperently doing a similar thing in regard to dropping out of lockup.
It only occured after about 5 - 10 km after getting in top gear. It would drop down a gear, then after a short time (20 secs or so) go back into lockup.
I suspected a temp sensor(and still do) or throttle position sensor.
Now it does what your wagon seems to do. After running in top gear for about 10-15km and only at speeds between 85kph and 100kph it will give a short "shudder" or "growl" and the revs will bump up then it will settle down to top gear.
It occurs at about any throttle opening either on the flat or up hill. I am not sure if its an electrical problem with the auto computer but will have to investigate further. I have checked the throttle sensor and it seems ok.
I just had the oil in the gearbox changed (191,000k) and it still does the same thing.
If its not a elect. problem it looks like an expensive gearbox rebuild.
Its very hard to find any information on these auto boxes. I would have a go at doing it myself if I had the time but I guess I will just have to cough up for it.
Or better still trade it in on a manual. Never did like auto boxes anyway, its mainly for SWMBO.