I claim the ornamental design for a pallet puller, as shown and described.
FIG. 1 is a perspective view of a pallet puller showing my design;
FIG. 2 is a side view of the pallet puller;
FIG. 3 is a top view of the pallet puller;
FIG. 4 is a bottom view of the pallet puller;
FIG. 5 is a front view of the pallet puller; and,
FIG. 6 is a rear view of the pallet puller.
The broken line showing of parts of the handle is included for the purpose of illustrating portions of the puller and forms no part of the claimed design.