Could My.....

i would check the voltage at the battery and at the alternator. even aftermarket gauges see some inaccuracy/ voltage drop, etc. a DVOM used at the mentioned items will tell you more. check the book. for most cars, 12 volts at idle with no accessories is ok. that is probably optimistic on a stock fox.
the important part is if it goes up when revved to around 2K or so. the book outlines the test and specifications. you should have 13.5 or more volts when revved.

if it reads less, check the voltage at the alternator. if it is significantly more, that indicates that the cable from the alt to the solenoid is bad, causing a voltage drop. i doubt that is it.

you can have the parts store check the charging system. you can also charge the battery overnight and (assuming it is good), if the problem goes away, but then returns later, it sounds like the battery is being discharged/ not replenished.
good luck.

it sounds as thought the battery has not been getting cycled too much of late (with the rebuild and all). again, really charge it. they can show good volts, but if not charged or defective, they dont have amperage to turn the car over,etc.
might be easiest for you to take it to the parts store and ask them to check the charging system out. takes a minute and is normally free. you can check each component, but it may be more involved than you want to get. it is always a good idea to check the components they suggest as bad for yourself. and have them bench and load tested when you take them in.
if you get a new battery or alternator, have it load tested before you buy it. they can often be bad off the shelf. if it's the alternator, might be a good time to do a 3G upgrade. will help with just the problems you have.

were i you, i would take it to the store for a check out. also clean the battery terminals. are you sure all the ground wires were reinstalled? the ground situation is already marginal, but leave one off, and you can run into problems. insufficient ground, and everything suffers. just my two cents worth.
good luck.