Ok guys help me out. 1998 gmc jimmy 4.3
resting voltage on battery's is 12.9 volts. Engine running 13.5 volts on battery's 13.7-13.8 straight from altenator. First start of the morning battery's read 13.9 volts after 10 minutes of driving voltage drops to 13.4. At idle in gear voltage drops to 12.4-12.7 until I start moving again an it jumps back to 13.4. A few weeks ago it stayed at 14.2-14.6 volts. I have high output altenator 5 battery's and a 8500 watt stereo system. At highway speeds an radio playing voltage has dropped as low as 11.9 volts. All pos an negative wires are 0 gauge wire battery's are 6 months old altenator is 6 months old. Someone said it could be voltage regulator ? Any ideas folks ?