4th is overdrive and wont let you accelerate fast, if you floor the accelerator fully it will KICKDOWN to 3rd and accelerate the car fast and shift to 4th once you let off. If you press the O/D off button your transmission will not engage 4th (overdrive gear). The 4th in an Auto is like 5th in a normal manual.
what you said sounds completely normal
btw using cng?
another point to check is that your throttle sensor is calibrated to your throttle lever perfectly, our ullu ke patthay mechanics love to fiddle with the throttle stop screw throwing the sensor out of calibration.