Just a couple of updates. I ended up trying out a Stant 45479.
It has the exact same dimensions as the Cummins one except less depth and it operates at 195F instead of 182F.
Stant 45479 (195deg) next to stock 1997 12V Cummins (180deg) T-Stat - Album on Imgur
I've also read that the Gates 33039S is an option but I haven't tried it myself.
With the Stant, my gauge stays exactly at 190F while driving, and I actually get head out of the vents. It also seems like it fluctuates less, but the first crack open goes to probably 205F.
I have towed with this and had no issues with heat.
The best part is, this tstat is $8, instead of $50+ from Cummins.