Well tbh mate I don't know but if your pump is an inline pump maybe it needs a lift pump also? Or it's getting air somehow? Do you have a swirl pot?
Hook up a fuel pressure guage connected at the rail and see if your supply pressure drops when the problem occurs?!
D2 rear axle is on watts link, guess this is better than a panhard rod when articulating a lot at the rear as it won't cause the axle to move sideways on droop, but also I think the d1 setup is better for huge articulation, plus it would be much easier, personally I don't see why the A frame setup is a problem as it's pretty much a 4 link setup as is.
The front axle would be nice to ditch the panhard and then run 3 link. Do you use a ball joint/rose joint to allow for articulation about that 3rd link?
Tbh I'm no expert on suspension or how many links you need
I'm just concerned about my swivel balls BUT managed an off road day today without breakage, phew!