EYECORP1303

I have a 2001 se nissan pathfinder and recently the tranny slips out of first into second gear only when the weather is really cold. I took it to nissan when it wasnt that cold out and the couldnt get it to do it again so the service manager told me to have the tranny flushed i did then it drove great. this morning (15 degrees PITTSBURGH....GO STEELERS!!!) it happened again accelerating the transmission slipped out of first into second slightly shuttering the car and then it shifted smoothly again no matter how fast i accelerated. suv only has 75000 on it all highway always serviced on time and bought with 18000 from a reputable dealer. if anyone has any ideas any feedback would be greatly appreciated. GO STEELERS!!!!!!!!!!!