Help!! Spark Plug 5 Misfiring

Folks I need help. I own a 86.5 NA with 5 speed trans. Lately my Supra is missing specially when cold. I replaced the plugs about 10-12K miles ago. It does it for the first 15-20 minutes of driving. After that it gradually dissappear at high speeds, but as soon as I stop or reduce speed the missing comes back when I try to pick up speed and again dessapear at high speed. I performed troubleshooting and pinpointed the missing to spark plug 5. I switched the cable on plug 5, but still misses. I pulled the plug out and tested for spark. Spark is getting to the plug, but for some odd reason is not burning when cold. Vaccum lines seem to be ok. What can be the problem. Can it be the injector on 5. Why only when cold. Is there more fuel getting to 5 than to the others. Why only on 5. Is there a way to regulate the fuel intake to each plug.
Thanks in advance :banghead:

Something that temperature-dependent and cylinder-dependent almost has to be either valve-related, gasket-related (head or intake manifold), or ignition-related. If I was a betting man, I'd bet it was ignition. Other than the plug wire, the only thing I can think of that is cylinder specific is the ignition timing mechanism. Check the distributor cap and rotor for cracks and tracks. Check the gap between the stator and the rotor. I bet your problem is in the distributor.

Just for laughs, I'd do a compression check.