Temp

I'm worried about the temp in my tank. I got an under the tank heater and it's set to 90, my air gun when I stick it in the cage close to the bottom it reads about 86. I also got a heat lamp cause my room is so cold. I just got my snake and he's all over the cage. Could my tank be too cold? The gun reads 76 on the top of the tank but towards the bottom it says 86

You want to monitor the temperature UNDER the substrate.

Sounds like hes just exploring his new environment. Make sure you move the substrate and check the temp of the bottom of the enclosure - You need to have an accurate temp of the hottest point your snake can reach inside the enclosure. For my UTH, I have a thermometer probe on the heat pad in between the enclosure and the pad itself (On the outside) as well as regular temp checks of the substrate/bottom of the cage. Usually the one probe is good enough tho because if the UTH is only running 90 outside the cage, its safe to say that the bottom of the enclosure wont get higher than that. Therefor you cannot damage your snake.

Aslong as you have a hot spot of around 88-95 and have a "cool" end of the cage around 77-80, your snake should be fine. I would leave him alone for a day or two and let him get used to things.