14SierraZ71

Just curious if anyone has the same issue I've been having. So on the very first shift of the day from 3-4 my trans seems to slip into gear. After the initial run through the gears it shifts great every single time after that. I have real basic stuff done to my 14 Sierra..cold air intake, cat back exhaust and blackbear tune (yes the trans was tuned). It really seems to be temperature related because it gradually got worse the colder the nights get (I live in the northeast). And no matter how long I let the truck warm up before I drive it, it does the slip but only 1 time. Not sure if this is also related but the tuner said the torque converter locks after the shift into 4th gear.