Cat 3126 hard to start after sitting two days

HEUI cat 3126 cranks but will not start after sitting over the weekend unless you crank the hell out of it. When it does start it will fire on all but one cylinder and will run out of it and run fine after about a min of idling. replaced check valve on the back of the head, it was definitely bad but problem is still occurring with same symptoms. fuel filter stays full of fuel and oil is on the full mark. checked flash codes on dash and I get a 61 which I believe is overheat.
(we are a rural school district with 90% gravel roads, terrible place for a rear engine bus we constantly have to wash out the radiator and I replace the engine air filter every 2-3 weeks.)
Does anyone know if I can pressurize the injector oil rail and be able to see if I have a bad injector o-ring on the oil or fuel side? I believe it to be a problem with injector oil pressure but I do not have a scan tool to check pressure nor do I have a 6000psi gauge to manually check it. Once its running it runs just fine.

I didn't find the right solution from the internet.
References:

http://www.schoolbusfleet.com/forum/topic.asp?TOPIC_ID=40046

Demonstration video