rpa740tracker:
First, how much oil and how long (miles/Kms) between "getting low on oil"? Are we talking losing quarts here or just a quarter piint or less? Is it every 50 miles or every 5000 miles?
Have you had anyone follow you down the road when you "nail the throttle"? For example when attempting to pass another vehicle? Usually oil burners will blow some residue when loaded like this and the following vehicle can either observe or smell the residue/smoke (or even drops on his windshiled).
If the engine compartment is loaded with oil and sludge, first take it to a car wash, while its running carefully clean the engine compartment of oil and crap, especially around the covers and pan area. Don't hold the spray nozzle directly on electrical components. Don't neglect the rear of the block and oil pan.
If you have a leak on a gasket, you will have difficulty telling its point of origin if the entire engine is coated with road dirt and is greased up, so clean it off so you can see what is what. Using a mirror helps you to "see" the hard to get to areas.
If no leaks and no smoke are observed ....
Changing oil AND filter requires a little more oil. If you are changing your own oil, do you check the top off level to ensure the oil is topped off AFTER your oil and filter change .... right before you slam the hood down, park it and go get cleaned up?
And lastly, if you don't change the oil, do you take your truck to a "Quickie Lube" for oil changes? If so, do you check the oil level when they tell you "its all done! That'll be $21.99"? It is possible they are pumping in 3.5 liters/3.7 quarts (for just oil change) when it actually requires 3.7 liters/3.9 quarts to top it off for an oil change WITH filter.