oil heater, pump cavitating, what to do?

I had to move the tank 3 feet further down towards ground. So, now the heater pump needs to pull fuel up 3 more feet. There was already a long distance from tank to pump. About 40 feet. The tank was at the same height as the pump. fuel got pulled up about 5 feet, over about 30, then down about 5 feet. Its been working like this for 26 years. However, I had to move tank down 3 feet. So, its now pulling up 8 feet, then over 30 feet, then down 5 feet. However, now it keeps cavitating. What to do? Last resort is to move the tank back up. Someone said a small low pressure automotive fuel pump mounted at the tank to push the fuel. This work?

tks,
paul