Search:

I don't think that small amount of fluctuation is much too worry about, adjust for the highest reading and back off a tad until you can time it with a light for more accuracy.
4gauge so be plenty...

Too small primary battery cable, poor grounded neg cable, timing issues. Either one or a combination of the three. How far is the battery from the starter?

If this just started I would check the grounds and your connection at the solenoid.

A lot of times hard staring issues when hot can be caused by a number of things, too small positive battery cable 8gauge, IMHO, is borderline 6gauge and bigger is better. Rule of thumb, the further...

Check the counter weights under the module in the dist and make sure they move freely. If you have a vacuum gauge you can get the timing fairly close, adjust for the highest reading and back it off...

If you're having cooling issues at highway speed you have more than a fan problem. As mentioned I would have the radiator re-cored and back flush the block and use a good quality thermostat along...