Just like the title says. I have 2 new batteries and alternater (don't ask why long story). What causes this? Fix?

 

You won't believe this as I didn't. there was a thread about 2 months ago chasing this down. The guys chased grounds, switches, PCM everything. I had the same symptom. Heavy throttle and the lights would flicker, volt meter would drop slightly. I was afraid it was bad wire or my PCM.

One post saved the day.. I checked the connections to the Grid Heater relays. One night the truck was idling in the dark and I had the hood up. I thought what the heck, I will try to wiggle the relays. BAM, the relays would buzz and trigger!!! I cleaned up the connections on those cheapo elbow connectors and crimped them very slightly. I have had no issues since..

Give it a shot.. I was amazed..

J

 

I now have the same problem what was your fix???