Since he's asking about a FUTURE PURCHASE referencing an OLD TRUCK he NO LONGER OWNS, he's not asking how to fix the problem.
I have a 2000, and it pings. It only does it under a load on real hot and humid days, but it'll do it if I load the bed, turn on the A/C, and take off quickly. There's Seafoam treatment methods to fix this problem with my particular engine (Lima 2.5). I Seafoamed mine and cleaned the MAF with LectraMotive and the pinging vanished. It's not anything to worry about.
The Black Beast 5.0
Better to Have Horsepower and not Need it, than to Need it and not Have it!
2000 Ranger Sport - 5.0L V8 - 8.8 LS rear