Replacing Transmission Modulator Valve

I have a 1990 Ford Ranger 4.0L V6 and the 4ALD transmission.
I need to replace the modulator.
What is the best way to do this. I've heard that some people remove the
carpet and remove the plate in the floor of the cab and get to i that way, or can I work from under the truck?
I'd rather work under the truck but heard that things are tight with the CAT
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