[pokeymcsnatch]

Truck manufacturers measure fuel efficiencies to the tenths and compete on that. At highway speeds, ICE engines win over a pure electric system, so throwing in another conversion step hurts. For city routes, pure electric is better than diesel-electric.

So in general, the disadvantages of a diesel-electric system outweigh any advantages when you take a look at how trucks operate.

New trucks have "automatic" transmissions (not torque converters- they're more like automatically shifting standard transmissions), so no manual shifting required.

Somewhat related, but refrigerated trailers ("refers") often use a diesel-electric system because it's easy to plug in to shore power and cut the diesel engine.

[pixl97]

A fair portion of large work trucks aren't moving all the time but require running. This is what Edison is shooting for currently. Jobs that have a lot of sitting, such as piles of things (ironically) in the oil industry and things in Welding applications. Municipal trucks can benefit by running full electric in sensitive areas.

Pure electric just won't work for any sizable portion of trucks getting converted, grid requirements just can't be met.