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Mechanic is incorrect.....Computer is not set to a moderate climate and is not set to any type of specific conditions.

The algorithms used by each PCM is different for each engine and vehicle application, since engines are different and even the same engine in a different vehicle will have different demands. Primarily, the computer looks at the engine oil temp upon startup, compares this to the air temp sensor for ambient temp, then looks at how long the engine stays at a specific temp while operating. It also monitors engine RPM and a few other inputs, then constantly compares this information to the internal algorithms for the oil life monitoring system.
Running cross country non-stop on a nice summer day will allow for long change intervals; short trips in the middle of the winter will cause short change intervals, since cold temps and engines that do not get to operate for a period of time hot, will damage oil. Extreme hot condition such as engine overheating will also cause a shorter engine oil change interval. In addition, the running time of an engine at a normal operating condition over a period of time burns off any moisture inside the engine.

The oil life monitoring system cannot determine the type of oil you are using; however, the algorithms are set for a specific type of oil, in the case of the H3, it is set for oil that meets GM spec GM6094M. Using an oil of a lesser spec will not give accurate results, thus you could damage the engine. Using a more stringent oil life spec such as that for synthetic oil GM4718M, will also cause the oil life indicator to be inaccurate; however, since this type of oil is better, will last longer, and is not as affected by heat/cold, no engine damage will result. (The spec of the oil allows the programmers to know the oil life under all types of operating conditions; thus, the engine oil life monitoring system can accurately determine when this oil will fail inside your engine, based on your engine's driving conditions.)

In addition, the oil life system cannot determine dirt in the engine. The algorithms are made up for a closed intake system, with a factory spec paper air filter. If you are using a type of oiled foam air filter, or have a leak in the intake system that could draw in more dirt, the oil life system will not be accurate. Oiled foam filters are noted to not filter the dirt as well as a standard reliable paper filter.

Also, the oil life monitoring system does not care if you are off-roading or on a hwy, it calculates the same way.

(Should I also note that Mobil EP does not carry a spec for either of the above approved GM Specs?)