I'm attaching an Excel file I put together from an '89 bulid sheet Pete found and from the salesforce pdf eaglescout526 has.
If you filter on source you can see which codes are from which source, I don't think the salesforce codes are completly accurate.
There is also this on page 3 half way down from the 87 accessories guide.
Decoding_Combined.xlsx
The 8th position in the VIN is a "U" (1JTMR65UEJT133457), this designates it to be a Laredo, Metric Ton. If it was a "T" it would be a Laredo, standard payload.
And how about some pictures???