Audi 100 Transmission shifts late

Hi, I have an '89 Audi 100. When it is very cold out (Canada) the transmission will rev out at 5000 rpm before it shifts. After driving about 20 minutes, it slowly goes back to shifting at normal revs. Likewise, if it is not cold out, it doesn't have this problem. I read on one forum that there is an adjustment cable, someone else said it was the transmission gaskets that leak, and swell when they are warm.
Sure would appreciate any help
thanks