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.