My 90 535i (208000 miles) auto transmission has intermittant hard shifting. I bought the car with 157000 miles and going into 4th gear she slipped a little. So since then I've changed fluid every oil change (5000miles) and the filter every 20000 miles. Last winter the trans started shifting hard once in a while especially when cold. Now the hard shifts are comming more often but most of the time she shifts normally. Any suggestions would be appreciated? Would a synthetic ATF help? Thanks!