Hyundai Veracruz 0171 and 0174 Error Codes: Causes and Fixes for Misfire and Poor Engine Performance

My wife recently filled up the 2008 Hyundai Veracruz (173,000 miles) with gas, after which the vehicle began exhibiting rough idling, misfiring, and sudden power loss — commonly described as 'bucking.' It ran smoothly before refueling. After arriving home, we let it sit for two days. On Monday, when she tried to start it again, the engine ran poorly and was eventually parked. The vehicle had difficulty starting initially. During our drive to the auto repair shop, the check engine light activated. We arrived at the shop only to find they were closed — just another unfortunate coincidence. Interestingly, the SUV ran slightly better during the return trip of about 30 miles, though still not at full performance. After scanning the onboard diagnostics, we found error codes 0171 and 0174. These are related to fuel trim issues: 0171 indicates a lean condition in the intake system (too little fuel), while 0174 points to a lean condition on the exhaust side. Could this be due to using low-quality or leaded gasoline? I'm seeking advice on how to diagnose and resolve these codes, especially for a 2008 Hyundai Veracruz with over 170,000 miles.