Tim- that's the highest consumption I've seen yet! Unfortunately high oil consumption is a common issue with mostly 1998-1999 isuzu 3.2 & 3.5L engines. You've probably seen this, but if you research other isuzu sites, you'll see the suspected cause is inadequate drain-back holes in the oil control rings. The consumption seems to be mostly an annoyance & doesnt effect performance or reliabilty. Old design has something like 4 holes, new design has 10+ holes. On the old design, oil gets trapped above the ring(s) and burns off in the cylinder. Gets worse as the vehicle ages & the rings get dirty with age. If you are still under warranty, Isuzu will replace the short block if they determine oil consumption is over 1qt/1000miles. Make sure your PCV system is clean to keep crank-case pressure down. I go back to where you got your truck first to see what they can do. If they cant do anything, before I tore into the engine, I'd pull the spark plugs & soak the cylinders w/ an upper cylinder cleaner like marvel mystery oil, seafoam, etc..etc. I'd run a product like auto-rx (auto-rx.com) and maybe run a HIGH detergency oil for cleaning purposes. Check a website: bobistheoilguy.com. If you can clean those rings out to get them to drain the oil again, your consumption should drop. G/luck
Joel