Hello. I bought a used 2013 2500 HD Chevy 6.0 liter Vortec flex fuel truck. Had 75,000 miles when new. I did a transmission flush through chevy and the transmission has been great !!! Recently in -5 degree weather on start up and driving after, The transmission on several occasions after warming up the truck would shift ok and then as the shifting progressed near 3-4-5 gears, the shifts were slipping and almost feeling harder after the shift. Once the truck drove for about 10 min the shifting issues went away. I have had no issues with the truck since I bought it and the transmission only acts up in the severe cold (like we just had in the last several weeks here in Pennsylvania) after the truck sits for a while and is cold.  I replaced a TPS sensor when I first got the truck and all fluids have been changed. I also noticed with the bad shifting in the cold, when I step on the gas pedal to increase speed, the shifting is delayed and then kicks into gear or the throttle hesitates. It seems odd and only occurred so far in the really cold -5 degree weather. Any idea of what it may be ? or what I should do ? Thanks.