The ornamental design for a frontportion of an off highway truck, as shown and described.
FIG. 1 is a right, front perspective view of a front portion of an off highway truck showing our new design;
FIG. 2 is a front view thereof; and,
FIG. 3 is a left, front perspective front view thereof.
The broken lines of the figures showing additional portions of the front portion of the off highway truck are included for the purpose of illustrating environmental structure and form no part of the claimed design.