Fuel starvation can also be caused by a blocked fuel tank breather causing a vacumm to be drawn in the tank. When the surge is happening try and remove the filler cap and see if it hisses as the cap comes off.
This could also be a simple issue (not DIY simple) of the governor in the injector pump playing up. If it is it will worsen with heat as the tolerances all expand ever so slightly more.
But as said elsewhere, check the simple stuff first.