My car loses power when driving sometimes. Has new connects now and bat and alt hold 14v?

My car loses power when driving sometimes. We put new battery connections on a new battery and the battery hold 14 volt and the alternator holds around 14 as well. when testing them we dont see the volts dip, but if we shut the hood and i put it in gear and/or mess with windows or locks the volts inside the truck show me it dipping. plugs on alternator are rather lose but we made them a little tighter and cant tell if it fixes the problem or not. any suggestions?