Good afternoon, I need to know what type of oil I have to use for my GMC to change it myself at home. I asked the dealer but they did not want to give me the information, they told me that I had to change all the fluids, the engine, the transmission and the differential and the cost exceeded $ 800 dollars, and in reality I only want to change the engine oil for the moment, thanks for your help.At the moment it is barely 42,000 miles.