All the plug wires need to be in the same range. To check the compression in each cylinder you will need a compression gauge. To check compression, remove all spark plugs, disconnect the power supply to the ignition, or remove the coil wire, put the gauge in one spark plug hole, then crank the engine over 3 times. Do this for each cylinder. Inspecting for a vacuum leak is easy, you look the engine over for any hoses off and look real close where the hoses attach to the motor.
Heat tends to deteriorate the hose where it attaches to the engine.
A couple of other things I think need to be mentioned. I get a lot of e-mails about this. I've changed my oxygen sensor and it still acts the same. After-market parts do not work well for computer systems. Each system has specific specifications.