VTEC should engage around 5,400 RPM for an auto as far as I know but on the model you have it will not be that noticeable. Less noticeable on the SOHC models plus less noticeable on an automatic. You should feel a little more pull from the car. On the DOHC VTEC there is no missing it
Like said, if you are convinced there is no change perhaps your VTEC is not engaging. This could be solenoid, oil pressure etc. Best thing to do is to bridge the servicew connector on your ECU and that way any fault codes can be flashed to the dash which may indicate why its not working.
Let me know if you would like some further info.