If I sign up for the class am I guaranteed to be able to pass the class and receive my CDL license?

No

No, that is 100% on you to do the work and pass your test.

No, it's not easy! But if you do fail the test, you can retake the test free of charge and they "sometimes" offer remedial courses for you to take to brush up on your weak spots if you fail

Instructors and staff all give you the knowledge and skills to pass. Well worth it, and everyone is friendly.