after replacing outside faucet lost water pressure

One of those frost-free sillcocks (picture attached below)?  I wonder if you were replacing it after the winter season and just before turning the water back on. It's possible that if you are in the area with high mineral content in the water, the mineral deposits dried up when it was shut off for the winter and then got dislodged when you were replacing the sillcock. They may be now plugging your new one.

See if you can shut the water line off, remove the handle and undo the nut that's holding the stem which is going all the way down to the far end inside the house, where the seat of that valve is.  Remove the stem and see if there's anything blocking the valve. Hopefully some calcified debris will come out.   If I wasn't concerned that you'd flood your basement, I'd say take a pair of walkie-talkies and have someone on the inside open the shutoff valve on the line that goes to that spigot (while it's disassembled). As soon as you see water coming out of the sillcock (careful - it won't go into the hose!), tell them to shut it off again. Basically, this may flush any debris that's clogging the spigot and also will let you verify the pressure is there between the line shut off and the sillcock. It'll make a bit of a wet mess outside, so you didn't hear this from me, try at your own risk. I wash my hands! (pardon the pun) :)  ... 

This is not uncommon for those places with hard water.  Many times, I find hard water deposits and calcium in almost every water line I am working on or replacing.  As mentioned below it is important to make sure all water lines are free of this debris from time to time.  Is this one particular faucet or all of them?  By replacing one, you could have dislodged a piece of debris and it found another water line to obstruct.