I have a 97 Sierra, when I bought it it had a shift solenoid code. I went ahead and replaced both solenoids and put some Lucas in. It got much better, it would hard shift into D and R at cold start and would stay in limp mode. I realized that it only does it while cold, if I limp it to the store and turn it off, wait for 1-2mins, start up, and take off....It drives like a new truck, perfect\smooth shift no vibrations. After research, I replaced the ignition switch, again woth no change. Any help is appreciated...