charging problems
 

Hoping someone can help me with this...I have a 2000 s-10 blazer with a 4.3.I have put 5 alternators on my blazer in the past 18 months,each time they start out good then as time goes by the voltage starts to drop,then the diode goes out.I have checked all lead wires,all grounds,and connections.I replaced the rotted ground strap at the rear of vehicle with a 8ga grounding wire.I am running driving lights in front and utility lights in rear(connected to towing harness) lights are all grounded good and protected with secondary fuses/relays.The computer checks good,and no dtc show up in memory banks.The only odd things that happen that I notice is when i rev the motor up sitting in park,no accs on the voltage hand drops to 6-8 volts then builds back up,sometimes quickly,sometimes slow.Then sometimes i can be driving and hit a bump in the road and voltage drops,then builds back up.I have had this problem checked by 4 mechanics and they say they cant find it.Any help would help me alot.Thanks