Problem with temp, battery and oil gauges, speedometer erratic.

SOURCE: Speedometer erratic

I have the same problem with my car..It is the speedo in the car that is bad...check into getting that replaced it should work fine after that.

SOURCE: INTERMITENT SPEEDOMETER MALFUNCTION, OK FOR

Likely one of the speed sensors on the trans,and depending on year of the vehicle,some of the 90's models had the Vehicle Speed Sensor (VSS) mounted on the transmission.

SOURCE: 1988 Dodge D150 Erratic Speedometer

Unscrew the speedometer cable from the back of the gauge and from the transmission, take the cable out of the sheath, clean it off with carb or brake cleaner, oil it and put it back in. If that doesn't do it, replace cable assembly. If that doesn't do it, pull the speedometer gear out of the transmission and check for wear. Replace if needed.

SOURCE: green sports light blinks , speedometer needle bounces or doesn't

The transmission speed sensor is probably going bad, it's located on the bellhousing, back by the firewall, and has a plug with either 2 or 3 wires. This sensor controls both the transmission shift points and the speedometer, the only gauge the ECM feeds information to is the tachometer. This sensor isn't that hard to replace, but last time I checked the only place that carries them is the dealer. But I don't remember them being that expensive a heck of alot cheaper than an ECM. Good luck and hope this solves your problems, I think it will.

SOURCE: speedometer does not function properly. needle

A faulty vehicle speed sensor will cause this.
It's mounted on the back end of the transmission where the drive shaft slides into, near the top, it's just held in with a bolt, on the right side of the tranny, also has a wire connection.