volt gauge reading fluctuates on 1993 Buick Roadmaster

replaced the coil,module,rotor,distributor,wireset,spark plugs; however,the reading on the volt meter drops from 13.5 to 13 volts and the car starts to run sluggish.also the daytime running lights drains the battery so I keep them off. Is my voltage reg.going bad? I can wait an hr and the volt meter is back to 13.5, but ten mins of driving it drops again.

1 answer
Get the battery, alternator and battery cables checked. Something is happening with the charging system and any of these items will cause this problem.