Our new kohler bancroft handheld shower has very low pressure there was no problem in other bathroom shower nor on old showerhead contracter sayys "that's the way it is"n

There seems to be something missing. Did your contractor do anything else except replace the shower head? Try getting a large bucket and filling it up with the shower on full. The flow rate is supposed to be 2.5 gallons per minute. So 30 seconds, half that much. Measure what you get. There might be a washer at the shower arm or at the shower head that might be misplaced restricting flow? I'd first see how much water you are getting, and call your contractor back if its not right. If the shower valve was replaced, there could be problems with the install. First check and see if the shut-off valves are fully in the open position (all the way to the right). Good luck. I hope this helps. Bottom line, you should be happy with the work. If your contractor is not responsive, you can let him/her know you'll be telling everyone you know what a poor experience you've had.