try a belt driven pump ? some testing was done on a dyno were some pumps could not keep up when the engine was at temp could not push water threw when psi when up . for racing you should have a restrictor or a 160 stat . can be other things as well tune up ? fan may not be working or not very good the only help it will be is in the pits or at the line to help cool it. T may not have a very big radiator .have you added water wetter or purple ice .liquid ice to water ?