I know there's plenty of posts about hard starting in the cold, but none that exactly matched up to my issue. Starting off. GP, GP relay and batteries are all in working order. I ONLY have issues when it dips below 20 degrees (usually down to -10). If it's warmer than that, or I park in the garage, my truck starts like a champ. I've done everything I know with the batteries, and tried to jump start from another vehicle, with no success so I'm starting to look elsewhere. The engine does turn over, just doesn't start. Also, after going through the starting sequence a few times, the engine turning over gets slower and slower - very sluggish. I took my batteries to NAPA yesterday and tested good. I'm wondering if all my hard starts has worn out the starter, I just don't get why I would only have that issue when it's cold. Presently my truck is in the driveway taking up space and my mission in life tomorrow is getting it started. Any suggestions on different things I could look at? I appreciate any help.