'96 Mustang 3.8 With A Constant P0306 Code

Ok folks I could really use your help here. I just purchased a '96 Mustang that was throwing a P0301, P0302 and a P0306 misfire codes. Well the car is bone stock and this is what I have done with it so far in regards to making her run smooth again. I have replaced the upper and lower intake gaskets, new coil, new wires, new spark plugs and new injectors. Now I am just getting a constant P0306 code for cylinder 6 misfire. Now it used to run smooth on a cold start and then like a switch flipped in about 5 minutes the idle will go down and the thing shakes like a bowl of jello in an earthquake. I attempted to change out the computer with a salvage yard one but it doesn't have the same number on it and it starts and runs for about 2 seconds then shuts itself off so I took that one back out. I have read ALOT of forums and everytime I find the same issue I am having, they NEVER post the results on how they got it fixed or even if they did or not!! So I am to my wits end and I am begging for all you gearheads out there to shine some light on this sucker!!

Not to be an ass, but did you even read my post creektrack??

I will let everyone know that it was NOT a spark plug, coil pack, wires, injectors, intake or a vacuum leak. It was exactly what I thought it was in the beginning but didn't want it to be. IT WAS THE VALVES IN CYLINDER 6!!! I had the heads redone and it runs like a new car. So this for anyone that is having a misfire code. Do simple things that cost close to nothing(spark plug) then borrow, buy or loan a compression tester and that will tell you ASAP if the problem is the cylinder itself or an electronic part.

****As for vacuum leaks.....that would not cause a specific cylinder to throw a code.