ZX2 has trouble starting in cold

car has been starting more easily then it was right after i replaced the sending unit. i brought it to the shop, heres what happened. I go outside to start it to bring it down there. Doesnt start for shit, cranked it so many times that i had to jump it off the xterra, finally kicks over after cranking for like 10 seconds on the xterra jump. Get it down there yesterday evening. They looked at it this morning. Started fine everytime they started it, i stopped by around 11 to see the progress, they say its been starting fine, they give it a shot while im there, and it takes 2 tries to get it started but then kicks right over. They kept looking at it the rest of the afternoon but had no luck with it. I just went to pick it up, it started fine. Im pissed. My girlfriend has taken this thing to shops almost a year ago for this problem and the same thing would happen, it would start fine for them when she got it there. I am at whitts end with this car. I hope that it blows up one day and ends this all.