I have a "heater line" (no cab, no heater on mine) tank heater. They come in bigger wattage than the freeze plug block heaters do. It works well for me, 1 hour plugged in and it's ready to run. I have a cheap timer on my plugin, and it runs for 3 hours every morning, just in case it's needed. I know, wasting energy, but convenience/peace of mind is worth it to me.
Diesels get cranky as they age. As said above, injection system is the most common culprit, followed by compression. Neither is cheap to get back to new condition, and you'll likely never wear it completely out, so just let her warm up before starting.
>>>I HAVE NEVER BEEN A FAN OF STARTING DIESELS COLD IN COLD WEATHER, IT'S HARD ON EVERYTHING<<<
Friend of mine spent a ton of money on a Deere combine engine when it sheared the injection pump drive shaft trying to start it out in the field in 0° weather. Steering wheel holders with a can of ether scare the bejeezus out of me as well!
EDIT: if you add a heater, either block or line heater, take care to make sure nothing hangs out where branches, etc can grab it. I've replaced a heater or two because of not following this advice!