the symptom: engine idles a little rough. voltage meter will drop & engine stall

What is your question?

when i start the van i have to rev the engine to keep it going or else it will stall. i have to keep my foot on the brake while keeping the RPMS up so that the engine will not stall. on the freeway there is no problem as the van RPMS are up and the alternator is suplying juice; however when i slow down or take my foot off the acclerator it will want to stall and i see my voltage meter drop. i am at my whits end with this van. i replaced the battery and alternator yesterday,i have resealed upper and lower manifold gaskets, new spark plugs in the past 3 months, new fuel filter in the past year, new MAF sensor, new idle air control valve. i have no idea what would be causing this. please help me resolve this it is my only vehicle.