i was under the impression that even though both systems use different wires, they're both coming from the pcm.

in any event, i only know of one vehicle speed sensor on your car you have a nice little toothed gear on your output shaft, which moves through the magnetic field in your speed sensor. in turn, that creates a fun little step type signal, the frequency of which your pcm reads as it'* speed. one speed sensor, to the pcm, to your hud and dash.

if i had to guess, (this is a guess), it'* intentional if it'* not quite lining up. i've heard on many trucks, the speedo is always clocked fast to help truckers stay within the limits of the law unwillingly.

anyhew, it could also be the refresh time of the HUD. i drove a park ave ultra and a GTP just about side by side, and the HUD refresh on the ave was much slower - it took a rolling average over almost two seconds, while the GTP refreshed more frequently.

They're driven buy the same sensor in the trans case right abouve the differential. I wonder if swapping sensors would make any difference?