I'm still picking up the way this place is set up and should have posted here in stead of the XSeries area.

I've got a '97 XH ute, 6 cylinder and auto box.

When it gets into top gear (on an easy throttle this is around 70kph) I can hear, but more feel a rumbling that isn't present in any other gear.

I'm assuming it's the gearbox rather than anything else, but open to suggestions.

Any comments?

My latest search makes me think it might be the Torque Converter on lock up, is there any definitive test? And if it is the TC is it likely to die a slow and lingering death or fail catastrophically?

What can I do to fix it. And I mean me, I know the blunt end of a spanner from the pointy end of a screwdriver and mare than happy to delve into the unknown.