Hi, and welcome!
Glad to have you with us, but can you give us a little more information? What model do you have? Where did you place your box temp probe? I would be very surprised if you actually had temp swings that large, and there are explanations as to why you saw that, depending on what you tell us.
Now, here's the main question: How did your pork butt turn out? How big was it, and how long did it take? If the answer is it was great, and it took from 1-2 hours per pound, then my question to you is "what does it matter what the temp swings were?" The analog controller (I'm assuming you have a standard model, not a "D") are typically 10-20°, but your probe placement can give you false readings, big time. The bottom line is that if your meat cooked properly, in a "normal" amount of time, then all is good! Let me give you a piece of advice: Monitoring the box temp, on a standard unit, will make you crazy and add unnecessary stress to your life! If the food cooks properly, then let the smoker do its thing, and trust (as so many of us do) that it is "averaging" to the set temp!
Also, now that you've joined us, do us a favor and add a first name and town to your signature line; we like to know our new friends! And, head over to the Introductions section and tell us a little about yourself (BBQ experience, etc.). Nice to see folks follow good forum etiquette and introduce themselves to the group. We're here to help, and hope you a willing to join in the discussions and participate!