to drastically raise temps while mid-cook, add fresh unlight LUMP on top of your already lit coals.
if possible, stir it up a bit to get more lit in contact with the unlit (don't kick up ash though)
I try to grab a couple lit coals with coal tongs and put them on top of the unlit as well.
put the lid on in an offset way that leaves a 1" or more gap directly over the side with the charcoal.
after 5-10 minutes, you should be able to close the lid all the way and increase temps quite a bit
if you don't have 10 minutes, get a weed burner.
or have a 2nd grill ready.
or use a chimney (or mini chimney) to light a load of coals to add