what would cause my tach and speedo to be erratic after changing batteries

by joe
(walton,ky)

My truck stalled during idle took alternator off had it tested....tested good but batteries were bad I replaced them with new.

I started truck and it runs fine but now tach and speedometer are erratic and my truck is now goverend at 65 when it wasn't before I changed batteries......any ideas what would cause that!!!