A delayed, jerky shift in a Staria automatic often comes from fluid condition, valve-body/solenoid wear, or a sensor/software issue.
Check the basics first, and stop driving if you get severe slipping, a flashing warning, or a burning smell.
Why a Staria automatic can feel delayed and jerky
On a Hyundai Staria, a shift that hangs then engages with a thump is usually a sign the transmission is not managing pressure and timing cleanly. The common culprits are low or degraded automatic transmission fluid, a sticky valve body or shift solenoid, dirty internal passages, or a sensor/wiring issue affecting input/output speed and temperature readings. Software calibration and adaptive learning can also cause poor shift quality, especially after a battery disconnect or repair. On higher-mileage vans, worn clutch packs or a tired torque converter become more likely, but I would not assume the worst until the basics are checked.
