99 powerstroke hard to start

[mtmckiddy]

My 99 powerstroke would not start this morning. Not plugged in. 25 degrees for the low. Finally start after a long period of trying. Wouldn't even hit and die like usual. Usually starts better 10 degrees colder. Glow plugs were replaced last year. Tested relay to glow plugs today and seems to be working properly. What am I missing. Any advice would be appreciated.