the plugs are new...i checked them. the wires are new and none fried or shredded. all hoses and clamps are attached and tight, the oil is good, coolant is good. i put in a can of seafoam and that seems to be helping the way she's running. i do have a leak under the truck, maybe differential? would that cause misfires? i think it may just be a gasket?

 

Oxygen sensor is still my guess.

 

How often do you need to put coolant in it?

I would replace just those three wires with some wires from the autoparts store and see if that helps.

If it does help, then put on a full new set of wires.
8mm thick or better.