Tune changes

Well ive been have a little problem with my tune, the truck would start up but go to a really low idle and the stall saver would kick in to make it not stall. So i did a little tweaking on my tune for the start up and flashed it in the truck. It seemed to be the fix the truck started right up perfect every time, well i get in my truck this morning to start it to see the how the cold start up was and it was fine, but once the motor warmed up the tune i thought fix my start up sucked, it would bearly start. so why would last night the truck start up great then the next day it start crappy on the same tune.

BTW: the truck was on running temp both times.