At 78 pounds cold, or 80 pounds cold, once you start down the hiway they both will be above and within operating range.
On my 2005 F350 King Ranch, Long Bed, Crew Cab, Dually, I ran the flexible metal mesh extensions. What a time saver they were when checking. Unfortunately I did not have pressure sensors so I don't know about the application on the extension.
If you do get the extension you may not be able to secure the extension to the wheel with the anchors supplied for the chrome allow rims. I just let mine "hang" and since the wheel is turning the extension just turned with it. In one years time I never had one area of noticeable rub wear.
Edited: I also would never be without a Truck Tire Pressure Gauge,
similar to this and of good quality. It makes checking that inside dual so much easier.
I would only use metal mesh extenders.