You reminded me of another US example. Never worked very well, and electric operation was severely limited, but there *was* the UA Turbotrain in the 1960s-early 70s that was used in NY-Boston and Canadian corridor service. Primarily gas turbine powered, and its "high speed" operation was all in that form. But it had 600V 3rd-rail capability for NY local operation. Train itself was a Talgo-like affair with a reputation for being very hard-riding and noisy.

While technically "high speed" - operated at 90mph or more in service, and tested at over 150 - this is hardly the model for HSR as presently envisioned.

There was also a Bombardier "Jet Train" - intended to provide Acela-like service on non-electrified lines - but I don't think it ever went into service anyplace, if in fact a working demonstrator was even built.

Oil prices skyrocketed in the 1970s and pretty much killed off the gas turbine schemes. They're the only way to get enough combustion power in a small space with reasonable weight to make actual high speeds work in a non-electrified vehicle, really; diesel just can't do it. Unfortunately, turbines tend to be maintenance intensive and fuel hogs.