. Could it be that the fuel pump is dumping too much fuel?.
no, the mark 8 uses a "return fuel system" controlled by a fuel pressure regulator.
the regulator opens and closes and keeps the fuel rail at a specific pressure by varying the amount of fuel that is "returned to the tank".
Simply put.. you have increased the volume..but unless you increase the pressure via an adjustable regulator then you haven't "added more fuel" per say.
The presence of water in the exhaust is normal but also can indicate a rich condition.
The normal operation of the cats turn unburnt hydrocarbons<--gas into water vapor.
That water vapor depending on the amount could be normal, or could be a sign that it's running "pig rich".
your best advice would be to contact Lonnie and follow his steps to the letter.
This isn't the time to get information from message boards and use it to debate with the tuner.
you will get futher, faster by simply following what lonnie says.
Back to the fuel pump.. the reason the 255 is an upgrade is not because it puts out more fuel. the real benifit for most comes from the fact that the pumps output can degrade a WHOLE LOT before fuel delivery becomes and issue.
if you take a 190LPH pump and a 255LPH pump and they both lose 10% a year, it doesnt take a rocket scientist to figure out the 255 pump is gonna perform better over the long haul.