Well I've gotta ask.. What all have you replaced since throwing the P0172 & P0175 codes? Those codes are usually tied to bad O2 sensors. Do you by chance have headers? Maybe you've got some bad MIL eliminators? Have you checked for intake leaks? Have you taken any of your intake apart for cleaning/maintenance? Maybe you've got a bad gasket somewhere. You might try cleaning your MAF and replacing your IAC, and then resetting your computer.
If your fuel pump was going out, you'd probably be able to feel it. Generally at 1/4 tank and under, the car will buck under acceleration. If this is the case, you won't be able to use the Focus SVT pump, as it is for returnless fuel systems, while the 98 CSVT has a return fuel system. You can get a Walbro pump to work, or I'd just stick with stock if you are lightly modded or stock. Hope that helps.
Mark
