A rebuild might help, I have been reading about a number LB7's where the rebuild is just not enough as the filter/primer head is just plain wore out due to age and use. A foot of hose and a new assembly for around $120.00 on Amazon (shipped and sold) no less with a new filter may be your ticket, they also have the rebuild kits to boot
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Genuine GM 12642624 Fuel Filter
Fuel Filter Base Seal Kit For 6.6L Chevy Duramax Engines
Dorman 904-124 Primer Fuel Filter Seal Kit