I think I know what it is. I have seen this before.
Sounds like you may have a sticking plunger or two in your injection pump.
Try loosening all 12 bolts holding your plunger housing in place and retorque them. It may be beneficial to rack them as well.
If one bolt is tighter than the other it will cause symptoms like this.
My only other suggestion is clogged and weak injectors or your lift pump. Those have probably been said previously though.
I’m willing to try that, I’ll try loosening the bolts and retorque them, what’s the torque spec on them?
I’ve been reading up a bit on racking them this eve. Would like to try it but little nervous 😬.