For what it's worth I seem to have an oil burning solution.
I picked up a very clean 2000 Trooper with a blown 3.5 engine on the cheap. My son picked up a 99 Rodeo 3.2 in great shape with a blown engine. Both around 100k miles. The papers are full of them. They seem to run great, start consuming oil like crazy, someone forgets to check oil often enough and boom. Well we are both mechanics, I worked for Citroen for years (years ago) and have been a mechanic ever since on all kinds of industrial equipment including major troubleshooting and he is in his 4th year of ME. We got both these cars to convert them to diesel but copped out and went replacement gas so we had to solve the oil issue.
Now to the point.
First thing I noticed when we started analyzing what was killing these engines was the way over aggressive pcv system where they not only vent one head to the primary side of the intake butterfly (that's good) but they also create a huge suction (and in our opinion a huge mistake) on the secondary side straight into the intake plenum where during deceleration there is a very high vacuum thru a 3/8 inch hole. Under high revs engines create what is called windage where the air in the engine gets heavy with oil "vapors" from all the flying around mechanical parts. Well if you create huge amounts of air flow thru the engine and into the intake manifold it carries the vapors (more like billions of droplets) right into the engine and what doesn't get burned in the cylinders ends up getting burned off by the cats. This is why you never see any leaks. The oil just seems to disappear. We absolutely proved our theory (to us at least) when we opened up the intake manifolds of these 2 blown engines and the 40K mile engine my son bought out of a junk yard. There in the valleys and pockets of the intake manifolds sat at least half a quart of oil. This is also a result of the drain back issue where too much oil is collecting in the valve covers.
We modified the breather system so that a modest amount of air flows thru the primary side (low vacuum) and plugged the other fitting at the secondary side and placed a small model RC air cleaner on the right hand head breather port. This is more like the system from years past before all the pollution crap. After a few weeks of driving back at school he reported that the oil consumption was normal again (around 1 qt in 2k miles or even less), the odor of hot oil has cleared up and his Rodeo runs great. He has been driving it now for 4 months with no problems. I will be putting a rebuilt engine in the Trooper shortly and I will make a similar system for my $2500.00 rebuild. The rebuilder claims to be aware of this problem and claims to address it during the rebuild. I'm not sure we are both on the same page. He may be refering to the drain back holes and that could cure it as well but for someone who wants a quick fix I would give this a try. As long as you send enough air thru the engine to avoid condensation and carry off fuel vapors that is all you really need. The oil should stay in the engine where it belongs.
Facing the engine from the front the problem side is on the right. Remove the hose going from the breather hole on the valve cover to the intake manifold. Plug the hole at the manifold and attach a hobby shop rc air cleaner to the valve cover pcv valve. A 10 minute job that allows air to vent thru the entire engine. Run it for a few weeks keeping a careful eye on the oil level. I am sure you will be amazed. After the last of the oil trapped in the intake plenum passes thru, the engine will run and smell much better as well. No more smoke under acceleration also. Let us know if this helps.
I have seen many other major problems in industry turn out to be just this simple. I once fixed a large industrial washing machine in
under five minutes that had baffled the manufacturer and cost the customer and the oem thousands of dollars over the course of a year and a half. It was awesome! Pissed off a lot of engineers.
Good luck. Damn shame what has happened to Isuzu. I have always liked them.