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I don't think your having a air flow issue with the fan and shroud, I'm running a second gen fan with a 7.3 shroud with no over heat issues
FYI air flow is highest at the outer edge of the shroud on any mechanical fan setup with the most air moving out to the side at a 45 60 degree angle or more
We trimmed a 1/2" or 1 inch off my shroud just to gain better access to the belt tensioner without consideration on how deep the fan was inside the shroud
Here's the best photo I have of my fan and shroud spacing, the fan is still up inside the shroud, as far as shroud to radiator spacing everything is in it's factory position.

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Are you using a 1st gen or 2nd gen water neck, 2nd gen has a small air bleed hose to eliminate air pockets

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Mine's a ZF6 manual but it's been in the mid to upper 90's here while I hauled 20 loads like in the photo out of fields with no over heat issues

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Tell me about the thermostats you had and are presently running, were they both for 1st gen engines, there is a difference between 1st and 2nd gen thermostats
 

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I originally had a Napa stat in, have it sitting here it just says motorad 180F. I read about a lot of people having issues with aftermarket t stats so I called cummins, gave them the engine serial and they gave me the part number below which I ordered from Geno’s. The cummins t stat has a piece on the back that fits into the block (bypass?), the Napa did not have that though there was zero change in cooling. Also the cummins one has 2 jiggle pins that I placed at 12 & 6.

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That should be the correct thermostat, the disc on the back closes off the coolant bypass once the thermostat has opened up if installed correctly, the 2nd gen stat is shorter and won't fully close off the bypass allowing hot coolant to recirculate back through the block, at idle this would cause a loss of some coolant flow to the radiator
A 2nd gen stat in a 1st gen the disc would hit the block before the stat could fully open, not good.
 
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