I have a few tricks for Roosa Master pumps that might help you. When the ignition is on, make sure that there is 12 volts going to the pump whenever the ignition switch is on. The delivery valve inside these pumps will stick sometimes, especially if the engine has been sitting for quite a while (several months). If you have access to a mechanic's stethescope 'listen' to the pump in the area where the power wire hooks to the pump while someone turns on the key. You should hear a click, which means that the solenoid inside the pump is working and should be opening the delivery valve.
I am not sure where/how the transfer pump works on the 6.2/6.5 engine. Be absolutely sure that you are getting a good stream of fuel to the injection pump. It may help you to remove the glow plugs. This will let the engine spin over faster and takes some load off the starter. While you are at it (before you remove the glow plugs) ohm the glow plugs to make sure they are all good. There should be very little resistance (1-5 ohms) between the glow plug spade and ground. These engines WILL NOT start without at least some of the glow plugs operating.
If you are getting 12 volts to the pump but do not hear a click, remove the power wire from the pump and use an ohm meter to measure the resistance from the 12+ terminal on the pump to the case of the pump. I don't recall the exact resistance but 8-20 ohms sounds right. Open circuit=bad solenoid. This can be changed without removing the pump from the engine. If the solenoid checks, reattach the power wire and with the power switched on, use a small hammer and LIGHTLY tap around on the top cover area on the pump.
You really have to loosen the injection lines to get the air out of the system.
