99 freightliner problems

No telling. Might have gotten trash from the bottom of tanks. I’ve had rusty looking junk in mine. Had black floaties in filter from algae. I’m getting air in fuel from somewhere. It occasionally misses , sometimes throws fireballs, and excessive white smoke. Always worse when filters old. New filter, goes away for a while. Also only drawing from 1 tank. I think somethings blocking the pick up tube. Replaced all fuel lines. Still getting air from somewhere. Maybe a cracked fuel filter housing, maybe a leaking tank shutoff valve. They’re known for leaking. Cost about $500. Yours probably has one. They’ve been discontinued, replaced by just a T. I like being able to isolate each tank. I have the one that’s not drawing shut off now, it still returns fuel and will overflow otherwise. You’ll know soon enough. Might just be an isolated thing. Valve cover gasket need a dab of silicone in each corner on the block. You’ll see where the casting is uneven on each corner. Also a dab on each side where the cam housing is. The inside corners, front and back. A real thin amount across the entire cam housing doesn’t hurt. Not required. Orange, red, black silicone. Doesn’t matter. Orange is most common. Easily seen as being applied. Might need new rubber sleeved grommets. You can take them apart, see if the sleeves are damaged from over tightening. Sleeve avoids over tightening and cracking cover.