Kelvin, it was probably a little drier than expected because the smoker doesn't instantly cool to 140, even though you turned the dial down. These smokers are really tight, and it takes quite awhile to cool. You probably kept cooking for another hour.
If I'm going to hold in the smoker, I turn it down when my meat is 5° below target temp, then open the door for a few minutes after turning down to 140. You need to get that box temp down quickly, and the meat will rise to your desired temp through carryover cooking.