Its possible you got a bad membrane, I have heard of people getting them before.
Cold water will not slow it down that much.. I ran my unit on cold tap water from my well and with pressure that was 50 on the high and 35 on the low end and it worked well.
readings are not going to effect the out flow that much, my friend had a 700 TDS
and he could make water, he would burn through resin in no time...
I would call the dealer you got it from and see what thye say, my guess is membrane or something is hooked pu wrong.
A booster pump is a great add on for the ro