Crummins
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Comes with the necessary sender to work on these transmissons (4L60E and 4L80E, I would assume it'd work on the 700R4 as well.)
The sender goes into the pressure test port on the transmission. It's just above the shift linkage. Easy to remove and you only lose a couple drips of fluid.
The pressure test port works but isn't proper, the transmission pan is where you should be getting your reading. Also, if you have a 700R4, don't use the test port because it can block fluid flow and it not recommended.