Greetings Islandwhiteknight,
I happen to have the same 14-bolt under my '99 C2500, so your photos are visual confirmation.
For what it's worth, here's a drawing of the Dana taken from the C/K Factory Service Manual:
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Once you see a Dana, there's no confusing it with the 14-bolt you got.
Note: Back when your truck was made, synthetic gear oil was new/spendy. Interestingly,
there's a note at the bottom of this page concerning the Dana diff under 'extreme use'
where the recommendation is either changing the conventional oil every 3K miles (not a typo)
or, if you used the 75W-140 GM synthetic, you could extend the oil change intervals to 30K miles:
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Obviously synthetic gear oils can handle the high heat from sending big power through a 90° turn better than
the conventional 90 wt. NOTE: In a previous life I used to maintain night-vision (IR)
Litening Pods
as part of our Avionics package, and after a successful repair/Ops check at night I'd take a look across
the airfield at all the Civilian trucks servicing the airplanes, and I was always amazed at just how clear
and bright the ring & pinion gears would be visibly 'glowing' under the trucks. I don't know exactly
what percentage of hp/torque is left behind at the 90° turn in the diff, but the resulting heat is the
real deal. I wouldn't have believed it if I hadn't seen it for myself. :0)
****
And if you are ever having trouble falling asleep, you can check out what Gale Banks has come up
with to keep differential lube cooler during heavy use:
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BTW, nice rig. Always cool to see a GMT400 busy earning it's keep like yours obviously is.
And welcome to the GMT400 forum.