While I do think some of the oil burning is PCV related, there is another theory than the several presented here - this is what Jerry Lemond, who used to train Isuzu mechanics, told me:

The 3.5L is a stroked version of the 3.2L. Because of the deeper crankshaft necessary for the 3.5L, the pistons had to have relatively short skirts to avoid impacting the crankshaft, leaving less room for piston rings. As a result the 3.5L pistons only have one oil ring. The oil ring's job is to squeegee oil from the cylinder wall. The oil ring also has drain-back holes for any oil that gets trapped between the oil ring and the compression ring. The oil ring for the 3.5L only had 4 drainback holes, which apparently was inadequate for the job, so some of the trapped oil ends up going the other way, up into the combustion chamber and is burned.

The improved design 3.5L, identifiable by the screw-in PCV valve, has oil rings with additional drainback holes.

[shrug] I dunno which theory or combination thereof is correct, just thought I'd pass this one along. Have a nice day