To keep it cooler you need to get more airflow over the radiator and A/C
condenser.  One way I am in the process of doing is adding a 7 bladed Audi
fan and fan motor (my stock is going out).  It is going to increase the
surface area of the fan blades a bit.  I am also going to be adding an
inline fuse on the large red wire. The 7 bladed fan is too big for the 304
mm VW fan housing, so each blade needs  to be trimmed a bit to fit. I think
the Audi fan is @126mm.

You also need to control the heat absorption that comes from the front
radiator.  This helps to reduce the heat that the A/C needs to remove. I am
also going to add some heat blocking material under the front on the front
firewall to block the heat from getting into the front.  I need to seal off
the area under the front accelerator pedal.  Mine was measuring @137 on a
100 degree day.  Front firewall was about @125 and the floor was @115.  I am
also going to add some heat blocking material to the engine compartment to
reduce the heat coming into the van from the engine compartment.

If you do not have window tinting, add some to reduce the heat reaching the
interior.

Also, how long has it been since you changed your coolant?  Should be
changed about every two years.

Robert