I owned one for almost a year. Bought it brand new and sold it at 17500 km. Had Bridgestone B70 tires on it, 165/65r12 (I am not sure if it was 65 profile or 60).
Extremely well kept and maintained, but the vehicle never went above 115 kph on CNG and on petrol it seemed like it could hit 130 kph but I was too scared to attempt it. The vehicle sways too bloody much at high speeds and although i am an aggressive driver, i am not stupid :P.
I have also heard people hitting 140 kph on CNG, in the early model Alto's, mine was early 2009 model.
After many failed attempts I realized the vehicle could not go faster so I tuned my driving style to fit between the 80 kph to 100 kph bracket.
Try braking hard at around about 60-70 kph, the way this vehicle loses traction at the front end is almost hilarious. I would suggest the 80-100 kph slot for driving this vehicle. Even if you could manage to make it go faster kindly do not attempt it, at least regularly, as this Pakistani Alto is not designed for such speeds.
Regarding workshops, by my experience MiniMotors are the best. There location may be deceiving, but don't judge a book by its cover.
BTW regarding the choke cable, i think you've been had as the same thing happened to my Alto but the issue was rectified by adjustment rather than replacement.