I live in KL and i usually recommend two days, go to Melaka for a day, maybe overnight stay if you want to eat more, Penang has much to offer and is a compact place with much less traffic and even better food than KL, go to Langkawi, Kuching, Kota Kinabalu, but KL?? Unless you like malls and shopping!!
And if public transport can't take you were you are going use Uber or Grab, taxis no way, and if absolutely needed use one who turns on meter! Few weeks ago there was a story about french tourists charged 800rm for a trip which should have been around 10-15rm but the driver even took them to Putrajaya (thats 40kms away!), obviously there is taxi drivers who are honest but better be safe than having a surprise!