CM871 fuel pressure delivery

[Skinny6]

I have a 2009 389 with an ISX600 cm871 in it I have been getting the "fuel pressure delivery" warning on dash and when it comes on the truck runs like it has a big cam in it. It will also when going down the road go limp like taking foot off accelerator for 3 to 4 seconds with red shut engine light and amber engine light on then they go out and truck runs normal again. The truck is hard to start as in just cranks and cranks and now to the point of needing a little ether sometimes to fire up. Any help would be appreciated I have had it in a couple shops and nobody has been able to help much as it does it at no specific intervals except for the hard start which is regular now