Trick I had to learn...don't use the guru to get up to temp. Let the smoker do the work by using the vents to control your fire. When it is up to temp then put the guru on. With the drop when you put the meat in your guru may be overshooting your target temp. When this happens you will have too many coals burning, this the higher temps. You honestly should not even be worried about the drop. That is normal and will correct itself if managed right. aiming for 250 you should expect to see fluctuations and 260 is negligible.
Backwoods Fatboy, British Racing Green Thermapen