Malaysian roads are usually excellent, but the same cannot be said of driving habits or signage. (KL and its expressways, in particular, are notoriously confusing.) I'm not sure about your experience level, but a European friend of mine -- who used to drive a taxi for a living and whose idea of a fun holiday is to zip down from Scandinavia and drive around Spain -- found it rather harrowing at times. Don't drive at night if you can help it. Also, large chunks of Taman Negara are only accessible by 4WD or riverboat.