You want to look into mainly two things... one the EGR valve again, and second a possible lean fuel condition; which might be due to a defective emission sensor such as the oxygen sensor and/or mass air flow sensor.
Driving your Geo Tracker for longer period of time before the next smog check is more than likely not the solution. It appears an actual emissions fault exists. Start with having a smog check repair station inspect the EGR valve for proper operation, including ensuring that there isn't any carbon build-up within the EGR passages. If the EGR system is functioning properly, they will then check for proper Fuel Control and possible vacuum leaks.
Read more on what causes vehicles to fail for high NOx. What Causes High NO?
