As a K3 racer, the karts at Sepang were originally in better condition than Sham Alam, but they are starting to show a few problems and a larger speed gap appears between the fastest and slowest karts.
But this will always be an issue with rental karts so we cannot complain.
The general support during the race day is very weak, unless you stop the kart on the front straight, you will not get any support. In most cases the support staff are not watching the track., I have been to Shah Alam recently for a few practise runs, and the support is at a much higher level. Also the fact that 90% of the track can be seen from the pit area makes their life easier.
In short I would support a move back to Shah Alam. Until CK improve the support at Sepang.