Toyota Repair: 1995 Toyota 4runner 3.0 v6 4x4 manual trans, toyota 4runners, spark plug wires

Question
I recently bought this truck and the check engine light came on. It seems to be running fine but has a decrease in power going up steep hills. I had it scanned and was told to replace the o2 sensor which I did and then I reset the light. It came back on after about 20 miles of driving. I had it scanned again and emissions tested. This time I was told no codes came up but the hydrocarbon numbers were very high at idle, going from 400 to 1200 but dropped to normal when revved up to highr rpms. They said the o2 sensor and the cat. conv. were working fine. I took it to a mechanic who scanned it and told me it did have a code for too lean. He checked it for a vacuum leak and said it didn't have one but he adjusted my idle and timing, turned off the light and said that would clear it all up. Well, the light came back on again after about 20 miles of driving. I then took it to a different mechanic who told me it didn't have a vacuum leak and it wasn't misfiring but said the person who owned it before me had a recent tune up and had used the right plugs but had used aftermarket plug wires. He said the Toyota 4runners had very touchy ignition systems and the problem was that it needed Toyota OEM plug wires. I don't mind spending the $110 if it is the problem but I have already spent around $250 on misdiagnosed issues so I am a little hesitant. Does this sound like the issue or, if not, do you have any suggestions. Thank you so much for your time, this is getting so frustrating

Answer
I don't think the spark plug wires are the problem, the lean condition causing high HC readings can be caused by a vacuum or intake leak but it could also be caused by a leaking valve or headgasket, I would recommend having the engine compression tested for this possibility and also have it checked for a leaking headgasket but dothe compression test first, the compression on all cylinders should be within 10-15 psi, any larger deviation may indicate a combustion leak, normal compression is about 170-185, this may vary slightly, the important thing to look for is if one or more cylinders has a big difference in pressure than the rest.