Remember that Isuzu considered it 'acceptable' for this engine to consume 1 qt every 1000 miles. So if you have to add a quart for every 3 tanks of fuel, it's not excessive. I don't agree however & was able to cut the oil consumption in half by replacing the PCV valve with an oil catch can and adding a vent to my oil cap.

Ditto on checking the oil when the engine is cold. That's how I've always done it (either in the morning before I leave for work or in the evening before I start my commute home). It's by far the most accurate means of a good reading.