My transmission makes a big clunk sometimes when shifting gears.

What is your question?

The transmission feels like it slips and suddenly catches the gear and it's a big clunk. Sometimes I get a couple clunks as it switches between gears. The longer trip I make, and as I go up hills the worse it gets. I have it in the shop and I have drove with a mechanic and he said there was obviously something wrong. However he wasn't the transmission specialist, the transmission specialist says there is nothing wrong. Ford still has the vehicle and I'm not sure how to get them to fiX this problem.