If you Drill out the hole in the pressure pipe outlet on the pump (after removing the pipe the connector will un-screw from the pump) by about 1mm then this makes the world of difference, Your flow will increase without a great loss of pressure and it should cure your problem without buying a new pump, Changing your resevoir for a larger one will also help in keeping your fluid a bit cooler, i Have found the plastic type landrover radiator expansion tanks work well as the pipe outlet's are just about the right size