#1
I just got a new pickup installed in my guitar a 'DiMarzio DP200 Steve Morse Pickup' if that matters... well now when i ajust my volume nob... it doesn't really swell the volume anymore... i can notice minor change in the sound, but when i get to zero it seems more like it's cutting out instead of fading. more like a killswitch than a volume nob...

the instruction that came with the pickup had some crap about it working best with Ernie Ball volume & tone pots and switches and such... could this be the problem why the volume nob seems to have a limited range now?
#2
Some pickups are designed to work with particular pots with the right resistance range. If you don't match them the tone can change or you get what you have now. You should consider changing that pot out to the recommended or similar designed one.
It's a fine line between clever and stupid.