no maria there is no way of improving the heat, apart from using butane instead of propane but the grills are still painfully slow.
you will see from my post regarding cadacs that we choose to use a cadac rather than the vans cooker for most meals as with 4 adults in the van even breakfast would take me most of the morning, on the cadac i have a full english for 4 done in around 20 mins and its much much easier to clean.
in our van we use the cooker to do soups and anything in small pans but we do use the oven extensively but even this we find if its says gas mark 5 then we use gas mark 6 and so on.