When I first accelerate, I lose battery power.

To be clear, you just bought a new battery and alternator, correct? I don't know what "just barely purchased" means, except maybe you went to the store to buy those items and found yourself $1 short and had to leave emtpyhanded... :) But seriously, go through all your connections and make sure they're tight and not corroded. During acceleration the ignition system will draw more power from the same charging system (i.e. battery and alternator) as the lights and other electrical components, and if it isn't working properly you will get what you have, dimming. Take it to a shop or auto parts store and get the alternator and battery tested again while in the vehicle. All the big parts stores do this test for free.