Check that the transmission is spinning freely and that the suspension moves without binding also.. check also that your tires are properly glued to the rims, re oil bushings, let motor cool..

Every 3 heats, i would say take it out for a bunch of motor spray.

No need to rebuild shocks between heats, unless they massively leak etc..
after every race is more than enough..
I tend to avoid using comm drops on black can or Mabuchi type motors, you always end up putting too much and they gunk up the comm more than anything.. natural lubrication from teh stock brushes should be enough on those motors.