I have a 97 Impreza L with the 2.2. Whenever the gas tank get below a half a tank, I get a hesitation just off idle. If I give it more gas it goes fine, it's just at low RPM. When the tank is full it runs fine. I don't have any codes on the ECU, have installed a new fuel pump, fuel filter, wires, and spark plugs. I have set the TPS and cleaned the MAF. The fuel pressure is about 26 with vacuum and 32 without. Any help would be greatly appreciated.

fuel filter and a good fuel system cleaning...

Get your prostate examined.