A fuel cooler on your return line is not going to completely fix the problem. The heat due to friction of the fluid going through the lines would be the only thing you fix and that wouldn't even be perfect. An in tank pump will help. The cavitation is from the fuel pump's suction pressure being below the saturation pressure (pressure where the fuel will change state for the given temperature) of the fuel on the low pressure side (assuming the fuel is vaporizing on the inlet side to your pump or in your pump, if it is after your pump then you have fuel system design issues, cover that later). To fix this, the amount of suction that is required by the pump to get the fuel to it (suction lift) needs to be reduced as it affects the difference from pump suction pressure to fuel saturation pressure. Even if you used an in tank or external pump mounted to tank below normal fuel level to feed your current pump it should do the trick.
Now if your fuel is boiling after the pump (not in but after it leaves) then your fuel system is too small for the fuel at the ambient temperatures. The heat added by the pump and by the friction going through the pipe would be causing the temperature of the fuel to rise above that of saturation temperature causing the fuel to boil. To prevent that the fuel system would have to be increased in size. Example: if you had 3/8" fuel lines then switching to 1/2" fuel lines would change to amount of friction felt by the fuel for a set amount of fuel flow. This concept can be seen in refrigerant systems for things such as refrigerators.
Previously you probably didn't have the issues because you were right at the borderline but the increased ambient temperature can put you right over the top. As for the increased current draw on the fuel pump I have no idea, it should be erratic if the pump is cavitating, no resistance to pump then normal, no resistance than normal.