My voltage keeps Dropping out

Hey guys I need help. I was driving down the road and my check gauges light came on and my battery's were showing that they were dropped out. I pulled over and restarted my truck and it went away. I started driving once again and it did it again! It is just staying right at 13 volts not going up or down then it drops out again. I checked all leads and I cannot see any fuses blown. Please help me