Although the GMT400 platform was introduced in the spring of 1987 as a 1988 model , the K5 Blazer , Suburban , and crew-cab trucks retained the earlier platform until 1991 .
The GMT400 platform was introduced in the spring of 1987 as for the 1988 model trucks . However , the K5 Blazer , Suburban , and crew-cab ( four-door ) trucks kept the earlier platform until 1991 .