2001 Chevrolet Silverado Voltage drop

The voltage drops off ( lights dim, fans slow down, etc ) and comes back up quickly. The problem happens when you do a short acceleration and let off gas, like driving up a street and stopping for the next stop sign. Does not happen every time. Can not get it to happen on a regular basis. Do not have issue when driving at high speed and come to stop. Battery is 1 year old. Cleaned all terminals and connections to alternator. Voltage at battery when engine is running is around 14.2 when a load was put on system ( AC, wipers, radio, lights ) voltage dropped to around 13.9/14.0 and stayed there. I am the only owner of this truck. This has happened off and on the life of the truck but seems to be doing it more often now.