Power Steering gearbox replacement

[3quartertime]

Hi all,,,

I have what I think is a power steering gearbox going south really quick. The truck is wandering badly on the road. I have a few direct questions...

Can the power steering gearbox cause instant failure? For example if I'm on the highway will it totally fail and I crash and die? Drastic I know but the truck is whipping around pretty bad with the trailer attached. Tongue wieght isn't an issue as it does it unloaded and rides pretty flat.

For a replacement should I go with a rebuild unit or a new one?

I searched and found

this
about the summit aftermarket one. What would be the difference? I read my maintenance manual and I believe it states that my truck has a varible gearbox now. Would I notice a big difference like a 1970 truck owner would?

Truck is:

1971 K20 350/350

Thanks!!!