2000 f350 7.3 cold start

My truck is hard to start during cold. 149.000 miles no previous service regarding glow plugs or relays. What is the basic service life of glow plugs and GP relays? Is there another area I should be looking as well? It starts fine if plugged in. Does cycling the "wait to start" help at all, if trouble starting in cold. I almost got stuck in the woods awhile back and need to get this thing fixed. What is the best manual for doing some of this basic stuff. Thanks!

The very first thing to check would be the glow relay.. GP's and glow circuit failures weren't as high on the later built 7.3.. Certainly not unheard of though.. But a healthy GP relay would be the first thing I check..

Thanks!! I will try that first