Very rough start now when outside air cold
2005 F-350 6.0L turbo diesel, Use to start with no issue in cold weather. Started okay at a -15 degrees a year ago. Now once temps get to 25 really struggles to start. I almost wear out the batteries to get it to start. At 40 degrees it starts fine. Once started it runs good and will re-start all day long. First start in the morning is an issue. If I plug it in it will start just fine as well. I have changed glow plugs and this did not fix the problem. Could it be the glow plug relay? I hope the PCM has not done something weird. Any advice would be appreciated. I am new to the forum and live in Texas so it really does not get that cold.