I do not know what a class b felony is because we do not describe them as such in Texas. Nor have you mentioned what the offense was, the sentence received, your role in the offense, whether anyone was hurt or killed, how much time you did, if you made first parole, if you had any problems in prison, why you did not get probation versus prison time, etc. etc. (You really cannot do all that here but the point is that there are MANY factors which come into play making a real evaluation of your situation impossible.)
In general, it is near impossible to obtain a pardon. However, I will provide you with the link to the form checklist from the parole board that is used to apply. Reading it may help you evaluate your chances: http://www.tdcj.state.tx.us/bpp/forms/FP%20App.pdf
Here is a press release from 2009 of pardons that Perry granted: http://governor.state.tx.us/news/press-release/14067/ And, here is the link to a list of documents that include pardons that Perry has granted over the years: http://governor.state.tx.us/search/results/?cx=003463821556383649006%3Af7d9hoewgqg&cof=FORID%3A10&ie=UTF-8&q=pardons+granted&sa=Search&siteurl=governor.state.tx.us%2Fnews%2Fpress-release%2F14067%2F#1401
Although I have answered the question to try to help you, you should consult with a lawyer in your area in person on the matter. In addition, my answer does not establish an attorney-client relationship between us.
With the information provided by Ms. Henley and your follow up information you should make the effort to apply. While your crime should not have been committed, it sounds as though you did a harder sentence (based on the facts you relay) than you should have and have since served your country diligently. A pardon is not easy to get but your circumstances are better than many. I am not sure of the likelihood of receiving a pardon but you should make the effort.
Good luck to you and thank you for your service.
Although my intent in answering this question is to aid you in the legal process, my answer does not establish an attorney-client relationship in any way. You should seek the advice and counsel of a qualified attorney in your community to evaluate your legal needs and to advise you. No Attorney-Client Relationship is created without the specific intent of both parties.