Engine sluggish, loses power and smokes, sometimes backfires

I have an intermittent problem with engine lagging power at the times. Randomly but mostly when decelerating and not all the time. What happens is that the engine becomes sluggish, loses power and smokes, sometimes backfires until I let go off the pedal and change gears. The. The power slowly returns but sometimes it takes a bit longer. Could it be possible that the engine exhaust brake could in the the stuck/closed position preventing the truck from reaching its full power and causing the symptoms as described?