Hey I've got a 2003 CTS that's showing P0171 and P0174. We found and fixed a vacuum leak but the codes are still there and the car is hardly drivable. We have put a new air and fuel filter into it and have cleaned the throttle body and fuel injectors but that hasn't helped either. Yesterday we discovered that the fuel pressure doesn't seem to be right, it idles at about 48 psi but when rpms are brought to 1500 the fuel pressure drops to 35 psi. We took it for a drive and the fuel pressure continued to drop until it got to 10 psi and at that time the car stalled and wouldn't start back up. This problem has been going on for about a month now and it's really starting to bother me and my dad, any advice would be great! Thank you!