Several factors limit the speed:
* Tire size and gearing: The specific gearing and tire size on your Jeep will influence the maximum speed.
* Engine limitations: The engine's power output will ultimately determine how fast it can turn the wheels, even in 4-High.
* Terrain and conditions: 4-High is intended for low-speed, off-road situations. Driving at high speed in 4-High, especially on pavement, can cause drivetrain damage.
In short: Attempting to determine a precise top speed for a 1989 Jeep Wrangler in 4-High is impractical and potentially dangerous. It's designed for low-speed off-road use, and driving it at high speed in this mode will likely damage the vehicle's drivetrain. Avoid doing so.
