Thanks... I've checked and I reckon the vacuum is intact, certainly at the inlet manifold. I guess I need to check where it enters the box.

I drove it to the golf course (only about 5km each way) this afternoon and it behaved pretty well. I'll give it a longer run tomorrow and see what happens.

I don't think it can be a dud trans when it goes so hard in 1st and second but autos aren't my area of expertise so any advice is cool.