My lumina with the 3.1 motor has a problem that i can't figure out. when pressing the gas pedel it lacks power doing only 15 miles an hour this problem last for about five minutes and then it picks up normal speed afterwards. any sugestions

Have you done a fuel system pressure test? Could have a partially clogged filter, keeping your system from building proper pressure right away. You could also have a bad fuel pressure regulator. You could also have a fuel pump on its way out.