OK..
you have to remember one thing about diesel engines... they run on HEAT
frankly, I'm suprised plugging it in for an hour is enough to help.
You've got a problem with one or both of two things...
either the glow plug circuit is still not working; Easy enough to check, put one half of your jumper cables from the positive side of either battery to the glow plug side of the relay (what you called a solenoid) for about 30 seconds. If it starts, you have a relay control problem. To check that you'll need a good test light, but get back to us on the quickie test... (thanks T-Bar for the idea)
if not, I'm thinkin' it's not whippin the engine over fast enough to create heat of compression; bad cables, starter taking a dump, oil too thick for weather conditions, something like that. Does the tach needle jump at all cranking? Go to NAPA or Auto Zone and get a cheap 1,000 amp AMMETER and tell us what the stater draw is...
so... quit throwing parts at that thing and start checking stuff and tell us what you found. We'll be here.
(well, maybe not me personally, I have to go to work and pull a 12 today; but you get the idea)