You are right. There was an M-715 which belonged to 2/44 out of Ft. Sill, OK, a Pershing unit. We were en route from Lawton, OK to Blanding, UT. It was snowing and I have a few pictures. In one of them, you can see the white M-715 which was a support vehicle for the launch site in Blanding.
You can see it in the first picture and in the background of the second picture. These pictures would be from very early spring, late winter, 1969, taken in Clovis, NM during an evening stopover.