Since no-one has answered your question in days, I'll push my memory to the max.
It's a chassis/frame/engine type code. On my phone so i don't have exact info handy.
Like standard cab/long bed or xtra cab/short bed, etc.
If I'm wrong I'm sure someone will jump to correct me.
Ya, I figured it might be something like that, but nothing references the number/letter combo. The other interesting thing about this thing is that the door tag states that it came stock with 225/75/15 tires, yet the diff code says 4:88 gear ratio. Couldn't imagine this thing with little tires and 4:88 gears, lol. Guess I could be reading it wrong but the code is G144:noidea: