Nothing you can drive your truck, but if you're doing routine maintenance you should probably change your oil, oil filter, oil pan drain plug washer, air filter, and PCV valve (most people don't but it's a 7 dollar part, that's amazingly easy to change, that if fails can cause, on average 3000 bucks) so it's your call, 7 bucks and a little elbow grease or 3000 bucks in the hole.
Usually this means you need rings
Screwed into the head. Follow the plug wires.
The gap on the plugs might not be gapped properly.
check your distributor cap and rotor, check the coil, check the wires, check fuses for ignition.
Spark plugs and wires
Changing the plugs and plug wires correctly has nothing to do with nor can it cause an oil leak.
yes
you have to change them one at a time this way you cant mixup the wires cap the plugs to spec this can be found under the hood on a sticker or in the owners manual
the next step would be the coil pack
I would replace the spark plugs after 50K, the wires and plugs again at 100K.
No you do not need to replace any plugs at all when replacing wires.
It is either out of time, or you have one or more plug wires hooked to the wrong plug. If you did not move the distributor then you have the wires wrong.