IS A 1987 CHEVY TRUCK DOOR INTERCHANGEABLE WITH 1988 K5 BLAZER?

No, a 1987 Chevy truck door is generally not interchangeable with a 1988 K5 Blazer door. While they share some GM lineage, there are enough differences in body style and dimensions to make them incompatible. The door openings, window shapes, and mounting points are likely different enough to prevent a direct swap.