I'd go over all connections ensuring there tight and looking for signs of corrosion at the battery and alternator. Pull the voltage regulators connector and ensure its in good condition and re-connect. Check the regulators mounting bolts. Check the ground strap to the chassis and engine block. Ground connections at fenders, rocker panels, etc.
If these check out ok, you might want to stop by one of the local auto parts and see if they can test the charging system for you.