Torque wrenches

I have a Snap On torque wrench for higher torque stuff. It is not the type where you crank the handle, it has a knob on the side with a dial that turns. Had Snap On guy that I know from the track check it, it is calibrated.
But...and this is me just overcomplicating my life..changed the trans fluid in my Allison trans. Pan bolts are 18ft lbs. My above mentioned Snap On starts at 50ft-lbs.
Any suggestions?