Oxigen Sensors

I already change the oxigen sensors on my rodeo 2000 3.2L, I did that due to error codes P0171 and P0174, But the problem remain the same.
What else i can do to fix it?

intake gasket leak will cause these codes also

Usually the ONLY time you want to change out O2 sensors, is if you have a slow or no activity code from them, or if you have tons of miles on them (like 120K+ miles). Like 2eye says, you probably have an intake manifold gasket leak which throws off the fuel trim, causing the lean codes.
G/luck
Joel

intake gasket leak will cause these codes also
Thanks guys, I'll check the intake gasket