When accelerating to get on the highway, the engine "missed" and the check engine light came on. The shop found a code for the fuel pump and replaced it. When I picked it up, they mentioned that the most recent start was hard and maybe I needed to check the battery. It started fine at first, but after a day or so, would start hard, but did not seem like the battery. Took it back to the shop, electrical system tested fine, and they said that it was a problem with the fuel pump. That was replaced again. Now, whenever the temperature is over about 70, it starts hard, especially with a hot start, but not the first start of the day. Is this another defective fuel pump or maybe some other issue?