Will 87 Chevy truck doors fit a 88 truck?

Yes, the doors from a 1987 Chevy truck should fit a 1988 Chevy truck. The body styles remained largely unchanged between those two model years. However, always double-check to ensure they are the same body style (e.g., both short bed, both regular cab, etc.). There might be very minor differences, but overall they should be interchangeable.