My ute is greedy

I OWN a 2005 BA Series II V8 ute that has done 30,000km. I have noticed an increase in fuel consumption from 14 litres for 100km when new to up to 21 litres/100km carrying the same loads and driven the same way. It also pings at low revs and has a noticeable drop in performance. I have had it back to the dealer who did a software upgrade that seemed to help temporarily, but on a second visit was told there was nothing wrong and that I should run it on 98 RON to stop the pinging. I did this, the pinging stopped, but the other problems remained. I have heard that Ford is aware of this problem, but have no fix at this stage. I emailed the dealer with the same queries but have had no reply. Could you please advise me where I can go from here?