2003 Ford Ranger Engine sqeals during acceleration and chec

I changed the spark plugs. Almost all of them had the gapping wrong (not my doing). Anyways the truck seems to drive smoother with the new plugs, and on the highway I couldnt get it to misfire. The check engine light is still on and the squeal is still there. Got home and had my roommate rev the engine while I tried to find where the noise was coing from. It seems to be coming from the back part of the engine and on the driver's side. The same side that cylinders 4, 5, and 6, which the diagnostic test said were having problems, are on. I dont think that the squeal is coming form the belt in the front of the engine. When in the driveway with the car in neutral I coult get the rpms above 3000. Went back on the highway and got the rpms up to 4100, but the engine didnt like it when the transmission shifted gears around 3500. Any Ideas? Are the things listed very difficult to fix on my own.

Is that hard to do and do you need special equipment to do it?

Thank you for your help, just trying to fix it myself.

I have the same truck. Had a very similar squeal about a year ago, 60000 miles. The squeal was from the exhaust manifold on the drivers side. The manifold from the factory was made from three pieces pressed together, and the leak formed between two of the layers. As far as the mis-fire codes, do you have any lack of power on acceleration? If so, you may have a plugged catalytic converter. Had that problem just recently. The plugged catalyitic converters caused back pressure and missfires in 4, 5, and 6. Just some ideas for similar problems I had.