thirdstreettito

1st digit = Nation of Origin
-- 1 = USA
-- 2 = Canada

2nd digit = company
-- G = General Motors

3rd digit = division
-- B = Chevrolet, incomplete example contract maintenance trucks
-- C = Chevy Truck
-- 8 = Multipurpose Vehicle All M1009's (blazers)

4th digit = GVWR/Brake System
-- B = 3001 - 4000
-- C = 4001 - 5000
-- D = 5001 - 6000
-- E = 6001 - 7000 Hydraulic
-- F = 7001 - 8000
-- G = 8001 - 9000
-- H = 9001 - 10000
-- J = 10001 - 14000
-- K = 14001 - 16000

5th digit = Line Description & Chassis Type
-- C = 2 Wheel Drive 1981-86
-- K = 4 Wheel Drive 1981-86
-- D = Military 4/4
-- P = Forward Control Chassis 2 Wheel Drive

6th digit = Series
-- 1 = 1/2 ton
-- 2 = 3/4 ton
-- 3 = 1 ton
-- 4 = Heavy Duty 1/2 ton

7th digit = Body Type
-- 0 = Sedan Pickup
-- 1 = High Cube/Cutaway Van
-- 2 = Forward Control
-- 3 = 4 Door Cab
-- 4 = 2 Door Cab
-- 5 = Van
-- 6 = Suburban
-- 7 = Motorhome
-- 8 = Blazer
-- 9 = Stake/Platform

8th digit = Engine Description
-- Y/S = V8-454-4BBL
-- R = V8-400-4BBL
-- L = V8-350-4BBL
-- U = V8-305-2BBL
-- T = L6-292-1BBL
-- D = L6-250-1BBL
-- J = 6.2L V8 Diesel (J code)
-- C = 6.2L V8 Diesel (C code)

9th digit = character is a check digit to verify VIN accuracy using a mathematical formula

10th digit = Model Year
-- B = 1981 F = 1985
-- C = 1982 G = 1986
-- D = 1983 H = 1987
-- E = 1984

11th digit = assembly plant
-- A = Lakewood
-- B = Baltimore
-- F = Flint
-- J = Janesville
-- V = GM Truck/Pontiac
-- S = St. Louis
-- U = Lordstown
-- 1 = Oshawa
-- 3 = GMad Detroit
-- 4 = Scarborough

That is the mostly full vin decoder. Please update original post.