erm... subject pretty much says it all...
i had been getting 30+mpg in my jetta (100miles per 1/4 tank), and recently
replaced the cable clutch mechanism with a hydraulic unit.  at the same
time, i replaced the front ball joints (suspension).
now i am getting 100miles per 1/2 tank.  i was curious if anyone had an idea
off the cuff what it might be.

my guesses are the following:
partially dislocated the cv-joint (but no binding when turning hard so i
dunno)
gas formula has changed (this has been talked about in here, but i'm in
maryland... far south of .ca)
tires were low on air (~15psi)
maybe the e-brake is slightly sticking (the light is not on however)

anyways, any help would be appreciated.
TIA,
~sudhir