Define "acting dead'. Be specific with your observations about what does or doesn't work and under what conditions the observations were made.

 

 

Probably a bad battery connection or cable. Start by cleaning the battery and cable terminals. If the battery terminals have been replaced by aftermarket terminals and they are painted, throw them away and either get some high quality ones made of brass or replace the whole cable.

 

After that 6-hour period when the starter won't turn does everything else work, like dash lights, headlights, blower motor, wipers, etc.?

 

A quick way to check if it's a poor termination at the battery is to take voltage measurements across the battery posts, the terminals, then at the bare copper you see where the terminals are crimped to the cables. These should all be about the same, but if you see 12.5 volts at the battery and only 8 at the copper or terminal, you have a bad termination.

As stated above, you should also check the grounds for cleanliness and torque. If corroded or loose, clean and torque the terminal appropriately.

While running, take voltage readings again as stated in the first paragraph. What is the voltage when idling? Have someone hold the engine speed at 3,000 rpms; what is the voltage?

Most importantly, stop throwing parts at it until you know what's wrong with it. Parts swapping is expensive. Grab a meter and get to troubleshooting. It's not a very complicated system so problems are usually pretty easy to nail down.