Probably you guys had some luck with your engines,but i also have two coworkers that have a 2001 rodeo & 2000 trooper,they do burn oil.
Some engines don't burn oil at all,others just a few & others a lot.
Remember that this 3.5L engine were all the same 'till 2002.
With the introduction of the 2002 axiom the 3.5L suffered significant improvement because isuzu redesigned the engine.