No Tach, No charging from Alt either

[FSecosky]

Hey there, maybe you guys can direct me. I just put a new Everstart 1000 CA battery in the truck 2 weeks ago. The truck was fine, until now. Last weekend my tach stopped working...then it flickered on a little, then it maxed out at 4k, then it just stopped altogether again. Then, I noticed my voltage getting lower and lower on the gauge. I cleaned up my battery connections when I replaced the battery, even replaced the ground to engine cable. (sidenote: now I don't think the autozone cable that replaced the OEM cable is quite as big, but it is probably a 2 gauge, instead of the 1/0, I hope that should not matter this much). So, did all that, then since I tested the voltage before and after the truck was started, I did not see an increase in voltage at all--so I and the parts store figured it to be the alternator. I replace the alternator, and still, no increase in voltage when I start up the truck, no change at all.

I have been reading on the forums about the voltage regulator being a problem--or in my case the PCM. Okay, if that is the problem, how do I test it, and how can i just install a new voltage regulator instead of buying a new PCM.

Also, I have been reading that the Crank Sensor could be bad, since the tach and alternator are not operating...is there a way to test that without going to buy a new one--or would my truck even run without the CPS working?

My voltage on the panel reads the first tick after 8V, and sometimes below. Also, the lights dim when I turn on my turn signals, wipers, or anything else electrical.

Please, any help is greatly appreciated, I am trying to avoid having to take it into the dealer...I try to do all my own work on my vehicles, being in college still and all.