I own a 2002 Pontiac Grand Prix GT with 79,000 miles. In the past year, I've started to have problems with hard shifts, and from what I've heard, this is normal with the amount of miles I've driven. What I've been noticing though, is that the car only shifts hard after the engine has been running a while. For example, sitting in sit and go traffic. If its cold outside (under 30 F or if I drive with out stopping a whole lot) I never have the problem. Is there any hope other than rebuilding the transmission? I've tried those fancy additives and they haven't helped.