Automatic transmission on 1997 Ford F 150?

Since new I have had this problem and took it to the dealer several times during warranty and told nothing was wrong. It only happens occasionally and only when I back out of my drive which has about 10 deg. incline. Sometimes if I have to wait on traffic and then back into the street and put it in drive it slips for a few seconds. I have heard that the dipstick on some Fords are not callibrated correctly. Is it possible that even though the dipstick shows full it could be a little low on fluid, and while waiting on an incline the fluid runs to the rear of the transmission? It only happens when transmission is not warm. Would it damage the transmission to slightly over fill it?