If you can't pass them, don't follow so close that no one can get around you then the truck.  I'll cut a truck some slack, because I've been there.  If they're averaging better than me, I'll follow them for a bit.  They'll soon pull away.  If I've caught up to them, I'll get around them and pick up the pace to not hold them back until my higher average takes me on down the road.  I know how fast I'm going to drive and don't adjust that.