I think most folks plumb the supply line to be 3/8" I know that when I shut the motor down it drains back into the tank and requires the pump to reprime each time.
I at first thought that there was indeed something in the tank restricting flow, but I have visually checked that it is clean since then. At first I was getting garbage out of it but now it's clean.
yeah, the external inline pump really get's hot sometimes, and after running it for a while it get's louder. I was also thinking about going this route:
then it'd all be "stock"