I feel that you have a very good and throu set of questions. I like how detailed it is and even though it is a bit long it goes though all the nessary question that you must ask. I would suggest that you work on your introductry paragraph. It seems confusing why you have instructions in it, I would think that you would just want to explain what you usalbity test is about and go from there. The instructions them selves if you were to stick with them are quite confusing also. I do feel like you have a solid set of questions though.

Overall excellent questions for a usability test. You cover all the necessary areas and go into enough depth to get good feedback from the testers. One suggestion I would make is to adjust the formatting to include bullets or numbers to segment off the sections of questions you had in the test. I also agree with the other comment in that the instructions are a little unclear in the introductory unless you are already familiar with the MATLAB program.