Voltage Issue
 

Have a 97 silverado with the 5.7. Have upgraded all power wiring to 1/0. Alt to battery, alt to ground, and battery ground. Also upgraded the largest battery I could fit under the hood from advance. Thought I was having battery problems after installing the subs under the rear seat so I added a batcap to help with voltage issues, but then noticed that with the radio off and idling different times my voltage was dropping to around 10v but I could tap the gas and it'd go back to around 14v. and also if I have radio off and lay into gas leaving from a stop and truck tachs to 4500 or above the lights dim alot. So I'm stuck between possibly belt slipping being cheapest fix, or what I really believe it is and that being a weak alternator? Alternator charges when I test it idling to a little over 14v but I have that issue when accelerating or when using the system. Anyone know a good place to get a larger ho alt if everyone suspects that to be probelm too?