If the controls are on the top rear of the unit, it should be a GEN 1. The Maverick probe should be as close to the position as the built-in probe so they are reading temperature from the same location relative to the heating element. Try that without the AMNPS being in the unit. In other words experiment using the instructions that came with the unit. The vent should be open to regulate airflow and smoke; the chip loader needs to be fully in, not half way. This is per the manufacturers instructions. And again, this is all without using or inserting the AMNPS. Get familiar with the smoker. Try a rack of ribs at 225 degrees. Get to know your smoker. As for the maverick, boil water and get a pan of ice water. Boiled water should register 212 degrees; the ice water 32 degrees. If it doesn't your Maverick is off. When the smoke dissipates, reload the chips via the chip loader. After 5 hours, enjoy the ribs.
At 225 degrees, a butt can take 10 hours or as much as 16 hours, depending upon the weight ( my experiences). 140 degrees is typically a keep warm temperature.