they were still making D100's up till 1989

 

Ahhh, did not know that (Obviously). I've never seen a D-100 newer than 78, tbh.
Was told years ago what I said above. :S Guess I was told wrong - again.

 

I believe that originally the 150 series was supposed to be the heavy half ton to maybe get around emissions laws and cayalytic converters/regular gas.

 

Thats correct I have a 1989 w100.

 

My 86 W150 had a cat converter on it when I got it (the key word is Had)..lol

 

I bought a D100 4 months ago that is an automatic. It is a four wheel drive. Has the 318 in it. Runs on air ride shocks that can be pumped up to make it go from a half ton to a 3 quarter ton.

 

You have a W100 then. There never was a 4x4 D-series.

 

It is possible to have a 4x4 D series truck. Not stock but think how many guys on this forum alone have made D series trucks into 4x4 or at least discussed it. There are a lot of non-stock trucks out there. I guess the argument could be made that this modification makes the truck a W series, just as the argument that the truck is what it was as first manufactured, but both sides of that argument have legitimacy.

 

About the same time Ford offered the F150 where before they were F100. I was told it was due to EPA emission standards. EPA standards were stricter for ½ ton pickups then for heavier trucks. By jumping the GVW a bit and changing the number of the truck they were able to produce ½ ton trucks without so much of the power robbing smog equipment.

 

Dodge and G M did the same thing.