The ornamental design for a tpostsupportstep, as shown and described.
FIG. 1 is a back view of the T post support step showing my new design;
FIG. 2 is a left side view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a front view thereof;
FIG. 6 is a bottom view thereof;
FIG. 7 is a top perspective view;
FIG. 8 is a bottom perspective view;
FIG. 9 is a perspective view in condition of use;
FIG. 10 is another perspective view in condition of use;
FIG. 11 is another perspective view in condition of use; and,
FIG. 12 is another perspective view of use.
The broken lines showing the T post and the cylindrical post are for the purpose of illustrating environmental structure and form no part of the claimed design.