Do you have a running tachometer in your truck? If so, download and use "Speed Box" (a GPS app) for your speedometer.
Craig
My '50 Chevy 3100 5 window, '62-235cu, 3:55 rear
My truck ....... Respect The Rust
If I'm not working on my truck, '65 m00stang or VW camper, I'm fishing with the wife or smoking Salmon.