At the track a couple of weeks ago my red Z28's tranny didn't shift into 4th gear on my 3rd pass. I believe I'm guilty of hot lapping the car cuz I had about 15 minutes between passes during the test & tune runs. My GM shop manual (page 7A-14A-38) has a chart of components that have a default action of "no fourth gear in hot mode". The components are working just fine now & did on the way home from the track that night as well. The only temp reference I can find is DTC 79...Trans. temp. > 302*F for 30 minutes (p. 7A-14A-15) which could not have happened that night. I haven't checked for this DTC yet but will in the next couple of days. I'm wonderin' what's hot mode & what activates it?