i have a 95 silverado that im using for a plow truck. i have installed a new battery and alternator..when i use the plow the voltage drops and the battery light comes on. even running the truck with out any accessories its only at 11.50-12.00 volts. any ideas?

 

95 siverado has a thumping sound under cab when hitting road bumps. new shocks installed still hearing it. any ideas?