Hi Here is my chevys story. 94 3/4 ton 6.5 turbo 219000 miles glow plugs all test fine starts hard when cold ok when hot has had 2 inj pumps. lift pump and oil sender work( lift pump pressure showed about 6 lbs cheep gauge)had a bad head gasket about a year ago fixed now. i dropped the fuel tank checked all lines hoses fittings. i put clear hose before inj. pump no air. ON return from pump no air bubbles (unless it sits over night)put clear hose on return from injectors and while idleing there is a steady stream of very small air bubbles. To my knowledge the injectores have never been replaced, is it time? Would anti freeze bother inj tips? I have run all the tests I can think of and read about. codes are dtc78 dtc 35 dtc 36
will miss at times under a load Steve

 

Injectors are good for about 100,00 -120,000.

They're past due at 219,000. No shame in it, they've given their money's worth.

The air bubbles you describe sounds like a small air leak somewhere in the supply from the tank. Small, but there....