Need Help With My Rec Tec - Mini Cooker

   I just bought a RecTec -Mini RT-300 and my first meat was 4 Smoked Chicken Quarters---which I cooked at 300 degrees on the temperature Display and when it got to165 degrees on my Maverick Probe I took it off and it was great.

      Then I bought a three & a half  pound Brisket . I set the RecTec  Temperature Display at 225 degrees and was hoping to take the Brisket off when it got up to  200 degrees on my Maverick Probe. . The first hour it went to 75 degrees --next hour it went to 105 degrees--the next hour it went to 135 degrees--the next hour it went to 149 --the next hour it went to 159 .I was satisfied for the first 5 hours -- Then it stopped going up in degrees on the 6th hour.I opened the grill's pellets hooper and put more pellets in it.I finally kinda gave up & raised the the temperature display from 225 degrees to 275 degrees & the brisket finally made it to 200 degrees on the probe around the 12 th hour.I saw smoke for the first 5 hours.

   I must have done something wrong but what happened do you think. What should I do now other than not  to smoke Brisket or anything else more than 5 hours.I wish someone here in Fort Worth could come look at it.

   This is my first time on this Forum and first time with a smoker.