Neither "customer use" nor "customer usage" is correct.  The customers are not being used; the trucks are.  I suggest the following:

>I am currently studying the patterns of truck usage by our customers.

Or

>I am developing a profile of how the customers who buy our trucks use them.

You can then add the following:

>We are interested in variables such as distances driven, fuel consumption, the number of years they keep their trucks, and the number of our trucks they have in their fleets.