JTryles & Matt400,
You don't need to use the metal back up brackets for any of the gauges on an A pillar or overhead mount. You use 180 or so grit sandpaper to open the gauge hole up just enough to still have a press fit of the gauge into the hole. If you mess it up, you wrap the gauge with a round or two of electrical tape. which bby the way works great if you have some light escaping the mount at night, just wrap the gauge case with black electrical tape to keep the light inside.
If you have an adhesion problem to the windshiled, it's because you need to REALLLLLLLY clean the glass with lacquer thinner, or prep solvent to get all the junk off the glass. If you have used an armour all type product even once you'd be amazed at the places the fumes get to in the summer heat and windex will NOT cut it. Even the fumes from the new truck plastics will need to be realllllly cleaned well, if done that adhesive tape will stay forever. You'll need a razor blade to get it off.
By the way we sell overhead mount customers the longer plug in leads for the gauges so that you have plenty of length and don't have to splice the gauge wiring harnesses, they are cheap and well worth it.
Mark @ DPPI