80 series gearbox

Hi all, Its been a while, I have a problem with my gearbox, when I am travelling at just above 60kmh I will be in top gear, when I take the gas off to corner or to stop the gearbox will change down the gears, before it would also do that but I would not feel it, it feels like I'm driving a manual because the gear changes are so prominent.
I changed the oil, that's all.
At the moment I am running stud-less tires because I'm in Japan and we still getting some snow and ice on the road.
Any advice would be great.
Oh and I did go to the Toyota shop and they just want to rip the gearbox out and have a look and charge me $2500.
On another side note, I had my starter motor changed for free as it was a recall item, don't know it this is a world wide thing, just thought I would let you know.
cheers