Weird Problem with my santro

Aoa! I need help regarding a problem in my Hyundai santro club gv (December 2006 purchased) car. The problem is that from the first day the car has not ran normally on patrol, but works really fine on cng. When car is on patrol and a/c is on ,it has absolutely no pick at all. But when run on cng it has pick and works smoothly .It literally drinks patrol . Yesterday i had more then half tank of fuel and the tank was empty when i had driven about 100 km on highway. the performance on patrol is like a car which is badly tuned on cng and when it is ran on cng + a/c with five people on board.

I had gone to three Hyundai (township, raiwand and sialkot) workshops showed them the problem .all of them do same thing. First they take test drive amd say yes sir u r right ur car has problem on patrol. Then they clean black sensor and the problem. The problem still remains there and they have same argument that when u will drive on patrol the problem will go. I have emptied many tanks but of no avail. Last time I consulted them I begged them to do something else instead of just cleaning the f*****g sensor and what they did was cleaning of spark plugs and then the same argument. On me getting little angry they said that on second tuning after 1000 more kms they will check the tappets , valves and injectors. But the services the Hyundai dealers provide is really bad as no one is bothered and willing to take headache for ur problem as mechanics there work on fix pay so they want to do minimal work. I want u people to suggest me any good workshop in Lahore or Sialkot. Thanks in anticipation.