Is there a need to prime it and how would you go about it.

Depends. If the pump has lost its prime, it is imperative to prime the pump, otherwise it won't pump.
As for whether it has lost its prime, you're on your own.

To prime, remove the front cover of the engine, remove the six or seven philips screws holding the pump cover to the engine cover. Remove the two gears, pack all voids with (I use) 90 wt. mixed with white lube, replace the gears, pack the voids in the gears with the same goo, reassemble and start the truck. Many suggest petroleum jelly, but I've found it to be too viscous and the 90 wt/white lube works everytime.

I've tried to pour oil back through the cooler lines, but Pendy was right, this doesn't work as the coolers are on the discharge side and this does nothing.

PT

Well I had to swap on a new cover, so yea I think it dry! ;)

I was thinking about the oil cooler lines prime, Thanks for the tip that it doesn't work.

What is white lube?

As some of you know, knowing a lot of English words does not automatically mean you know what they mean when combined into polysyllable combinations:
Talent bar is an example that springs to mind,

Or perhaps welding flies :flipoff2:

thanks
Tobias

Lithium grease=White Lube. In this application, I suppose that wheel bearing grease would work, as would petroleum jelly.

(I found the seal puller-probably where I put it!)