I have a 2005 Silverado with headlights that flicker. I have checked the grounds and all have been cleaned and tightened (none were loose). The headlights flicker when the engine is above 2000 RPM's and pulling a hill (under a load) and also when going downhill with the truck in a lower gear, again RPM's above 2000. It is getting worse. I have a new battery (July 12'). I changed the alternater thinking it was the regulator. This made it worse. Any ideas?