Looking for help with 2013 Chevy 3500 lml. Currently at a no start fuel issue. Purchased truck needing injectors which I have previous balance rates. Truck ran perfectly fine despite this. With Wanting to hold off until I was able to also do a cp3 conversion I just decided to rebuild and do new seals and orings and replace fuel return line. After replacing it would not start but had 5000psi at fuel rail while cranking. Only code that appeared was a p2296 which later went away. Kicked on for a second then redied where I found diesel in my oil and exhaust so I inspected cp4 which was fine no shavings or codes. But all 4 passenger injectors which were going out of balance rates (-.) now flooded cylinders at one time. Glow plugs are covered in diesel and fuel heavily dripped as I opened fuel lines and removed return lines. What would have caused all 4 to suddenly flow so much diesel at one time? Was told the return line would build its own pressure after replacing but saw someone else have to add air into part of line that goes into T’ portion of fuel return line by driver rear engine. What may cause and what should I test or do. Thank you!