Have a 2008 chevy impala 3.9L v6. The car intermittently will have issues starting. Car will turn over sometimes is acts like the battery is almost dead then you try again and it starts.

SOURCE: 2002 Chevy Trailblazer won't start

check the crank shaft sensor

SOURCE: 1997 Chevy Cavalier intermittent starting

I had the exact same problem on my 1998 Chevrolet 1500 c/k pickup. I also tried a new starter motor and solenoid assembly, but to no avail.

After weeks of searching for the problem, I found that corrosion had built up between the car battery terminals and the power cables extended from the car battery to the starter motor. I'm not sure if this is your problem, but it's worth a try. Also, check all other electrical connections, because these types of intermittent problems are often electrical.

SOURCE: 2004 Chevy Malibu 3.5 V6 engine start problem

When your in the car and it's turning over press the accelerator about halfway and it always starts right up.

SOURCE: I have 2003 chevy impala the transmission starts

Have the vehicle scanned. If you have a code in the computer for maximum adapt/ long shift, replace the EPC pressure control solenoid. This a real common problem on the 4t65e transmission.

SOURCE: I have a 2008 chevy impala. The car suddenly

ur vehicle is in limp mode[ a safe mode ] which will get u home trying not to cause any damage to engine --theirs a few reasons the vehicle will do this-low oil pressure-transmission problem-have vehicle scanned most auto stores such as auto zone / advanced auto [check ur local area]do this service for free the code gives u a start point towards resolving ur problem