GM-GMC: 2001 chevy express van 2500, jumper cables, ground cables

Question
My van will turn over but has a hard time starting, I have just replaced the battery, distributor cap and rotor, but I still have to jump start it with another vehicle and wait until the charge level with jumper cables has reached 12.5 volts before it will try to really kick over.

Answer
I will assume you replaced the battery with a new or a battery you are 100% sure is in good condition and is the same (or greater) CCA rating as the one removed.  That being said, it sounds to me like your starter is not getting enough juice.  If your battery is good, double check the connections at the battery, at the starter and the cables running from the battery to the starter.  Also check the ground cables between the battery and the block/frame.
Hope this helps.