hrs vs fuel consumption

I am trying to do the yearly budget and am cooming up to 33,000 hours on the engines, overheads were done at the 20k mark. the fule consumed is 777300glln mark on the 3512c we have. We have 750hr service limit, oil spinners installed. we are in a hot climate with decent fuel. oil samples are good no concerns.we do yearly injector and valve lash settings/ insoections. What do you guys base your intervals on fuel or hours?