how can Mings Black Pepper and Garlic Poached Tenderloin cook in 30 minutes at 138 and be a perfect medium rare. I cooked (4) 3 inch about 10 oz each and they were perfect. everything I read says it should have been over an hour

for some good reason they reached their temp quickly.  did you start with them at room temp and was it warm out?  had you seared them and not cooled them down first? 

@jselt53 Why would you want to cool the meat before you sear it? I have always taken mine out of the bath, dried any moisture and seared over high heat immediately.

How thick were the pieces? Thickness plays a key role in how fast a piece of protein cooks. Thin pieces are done very quickly.

If the thickness was 3/16 and the initial core temp was 41.0 degrees F, then it would take 32:17 to cook it. (water bath would be 138 degrees F). The meat would reach 137.9 degrees in 8:43.