Had same issue. Take the antena out of the truck channel and place it outside between the truck opening and the upper or top of the rear quarter panel. It will work great.

Typically change intervals should go hand in hand with driving habits and conditions. The more frequently you turn the engine on and off or are in heavy traffic situations I would change the synthetic every 5,ooo miles or same if the climate conditions tend to be more hot. In SW Florida it to me hot...