first thing to do is in the AM (cold) is to check if your GPR is working. Key off you will get on the one terminal (on top) will have power and on the other you wont. Untill key on with the WTS light on check the GPR to see if the other terminal now has power. If not you have a bad GPR and it will need to be replaced. in the meantime if its really hard to start you can jump the terminals to get the glow plugs working and then hop in and it should start right up like it did back before it went out.
Ill try to find a real write up and post it up.