John, morning and welcome to the forum...... If you have a "real" tenderloin, about 1" in diameter, they can be overcooked real easy.... If you have a "loin", they are about 3-4" in diameter and are more forgiving when it comes to cooking.... Both have little internal muscular fat and can dry out very fast.... overcooking is the main enemy of low fat meat...
On the tenderloin, I would smoke it for an hour or two at 140, then up the temp to 160 and insert a temp probe.... then pull the meat at 138-140, cover with foil, rest, and let the temp finish cooking the meat.... the temp should rise to 143-145 and you will be good to go..
Below is a time temp chart for beef and poultry... It is not for pork, but you get the idea of how time will kill stuff without overcooking it....
http://www.fsis.usda.gov/oppde/rdad/fsisnotices/rte_poultry_tables.pdf
Here is the FSIS Fact Sheet for pork....
http://www.fsis.usda.gov/oppde/rdad/fsisnotices/rte_poultry_tables.pdf
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[color= rgb(128, 0, 0)]Roll Call[/color][color= rgb(146, 144, 139)]/[/color] " and introduce yourself and get a proper welcome from our members.... Also, if you would note your location in your profile, it will help in the future when answering questions about smokin'... elevation, humidity etc....
We're glad you stopped in and joined our group... Enjoy the long smokey ride.... Dave