I can't find this exact issue when searching. I have a 1995 f350 cclb. My truck starts hard when cold like really hard unless I have it plugged in even in 40 degree weather. I figured it was uvch I did them both not to long ago but had a couple bad plugs so thought I'd check the glow plugs they all tested good but I needed to change the plugs coming from the wire harness on the motor side. The back passenger was melted on the glow plug end so changed the 2 glow plugs near the firewall on the passenger side just because. Changed both wire harness plugs and the ucvh on that side again. Truck still doesn't run right once it is warm it runs like a champ. No smoke starts everytime. Where do I need to start looking now.