A complete inspection is needed. There are many variable here but you can start off with fuel pressure and a scan of the computer. If you need to find a shop near you here, here is a link.
https://repairpal.com/repair-shops
Alex
RepairPal Certified shops can diagnose and repair your 2008 Isuzu i-290. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.