They had to add the "R" and "V" designations because from '88 to 91 they were selling 1/2, 3/4 and 1 tons in two different body styles. The new body style got the familiar "C" and "K" tags, and the old body style got the temporary "R" and "V" tags. When the last of the old body style trucks was built in '91 the "R" and "V" tags went away.
Not quite sure how the '87 got the "V" tag...unless it was built pretty late in the year.
Rene