I've seen a few GPS map setups for use as speedometers, but they tend to take time to sample the signal from GPS and use older setups. Converting from km to mph had me using a conversion guide I printed with a label printer and stuck to the trim around the gauge cluster. Not the most idea, but it worked... sort of. 2" lift kit, 13" tires and I wasn't getting accurate numbers as a result. I didn't want to big GPS nav unit on the dash or some smart phone sitting up there. I wanted a simple dedicated unit. And I found one. https://www.amazon.com/dp/B07HNDLGPC?psc=1&ref=ppx_yo2_dt_b_product_details This is a very small self contained unit that just plugs into the 12 volt accessory / cigarette lighter. I will want to permanently wire mine in, but I'm playing with placement currently. Right now it's sitting on top of the dash in the corner of the windshield. The display is small, but bright and just gives what info I want- speed, voltage, map direction. That's it. Yes, you can also do 0-60 times or braking times, but I just wanted simple speed. At $40, this small self contained unit was perfect. It updates faster than my phone or the Garmin unit did and has impressed me with its functionality. The perfect companion to ensure we don't go TOO fast in our lil' trucks. "What's that, officer? I was doing 75 mph? WOOHOO! I didn't think I could go that fast!" "It was in the drive through, sir." "Even more impressive!"