I have an older SnP Pro. I have never had a problem getting the temperature up to 300 degrees, and maintaining it. As soon at the temp would hit 275, I would add more lump charcoal, typically mesquite, and a handful of damp wood chips for smoke. I did notice that the temperature was higher/hotter near the fire box as opposed to the far end where the built in temperature guage was located. Consequently, I found myself periodically opening the smoker to rearrange the meat, and quite quickly the temperature would drop quite dramatically. Over time, I realized that I needed to have the charcoal and wood chips right next to the smoker for replenishing the fire box each time i Opened the smoker. Also, I would have to fiddle wit the fire box damper and flue damper to get the proper mix of air for good combustion, good heat and good smoke. A lot of fun in my younger days. More of a pain as I aged. But the results were very gratifying.
I now use a Cookshack smoker. Less hassle yet less fun as well. But I do enjoy the results.