2012 Ford F150 clunk when downshifting

when slowing down from 3nd/2st gear the truck would jerk and have a hard downshift and hear a clunk

Manual transmission? If automatic do you hear a clunk going from reverse to drive?

Look in the owner’s manual in the glove compartment to see how, then check the level of the transmission fluid.

Check driveshaft u-joints and splined joint & carrier bearing (if applicable)