Misfire cylinder 5
I took my truck into the Ford dealership to get an oil change, they were running a special- they did it for $17 (cheaper than I could have purchased the materials) anyway while the truck was having the oil changed I guess the mechanic noticed a noise and ran a check. It showed up as a misfire in cylinder 5. They called and wanted me to promptly give them $275.0 so they could tear the whole thing apart. They said it could be some spring (????) or a shot engine. . .
I hadn't even noticed the misfire. When I got the truck back yesterday I started tinkering. The misfire occurs right as the truck is starting up and that's all. A little bit of shaking a few pops and the truck is ready to go. I've recently done a lot of work on the truck including: replacing the head gaskets, ignition coil, wires that run from the spark plugs, new fuel filter, and water pump.
I'm at a loss about what could be causing this misfire. I have been reading and some people say check the spark plugs, but I am rather inexperienced at all this and I'm not sure what I should be checking the spark plugs for? Any other ideas?