This problem you are having could be anything in the secondary ignition system or a cloged fuel filter may also show up as misfiring under load. Typically a coil is the last thing I look for. Cap, wires, plugs are a little more likely. In my life time I have probably replaced about half a dozen coils. Only on two of those cars (Both Fords) was the coil really bad. The other coils I replaced I owe to my education in "Learning How to Fix Cars".

The best way to test a coil is with a scope. Short of a scope the next best thing I have found is a KD GM high energy ignition testor, which is nothing more than a spark plug with a ground clip on it and the center electrode removed so that the spark under no load has to arc up through the insulator and accross to the spark plug case. Place it on the coil wire first. If you spark is consitant accross this gap your coil is probably OK. You can also eliminate each wire or the cap by moving the testor from the center wire to each plug wire.

Be carefull when I got mine years ago 70's there were two versions "GM High Energy" With no center electrode in the plug (KD 2756) and the Standard ignition tester (KD 2757), for use in ignition systems with points (what are points?) or for lawn mowers. Both are available from mytoolstore.com for under $7.00.

For battery and voltage regulator, use a Digital Volt Ohm meter. With everything on if you have between 13.5 and 15 volts your fine. To isolate problems you might also want to get a clamp type (inductive) current meter.

John Roncallo