2001 Dodge Ram 2500 Diesel wont start

Hello All. I'm hoping someone can give some direction. My 2001 Dodge Ram 2500 Diesel wont start. Here is the scenario......Yesterday 1/12/2013 my truck started up fine. I drove about 15 minutes to my destination and I shut my truck off to open a gate and when I got back in my Truck it wouldn't Start. It was not cranking, the lights did not dim when I turned the ignition on, it just wouldn't crank over. I had full battery. I let the truck sit for about 25 minutes and then it cranked right over. I then parked it for about 2 hours and when I went to start it it fired up but I noticed at that time when I turned the ignition there was about a second delay before it engaged the starter and fired up. I drove the truck home parked it, turned off the ignition and tried to restart it but it did not engage the starter. Still had full gauges, I heard my fuel pump turn on but just no signal to the starter.
Today 1/13/2013 I did a few things but have not had any success. I first thought it was my Neutral safety switch, the reason is because just 2 months ago I had my Trani rebuilt so I thought maybe that switch was not replaced. Replaced switch and same problem. I then took my Starter off took it to the local O Rielly's and they tested my started and said it is good. Still have same problem. I have visually checked my fuses and all are good. I moved some of my relay switches around with other relays and still nothing.
Any suggestions will be greatly appreciated. Thanks for the site. I been helped out with other things in the past just by reading the threads.