I got stuck next to one of these in a 2 hour jam (something big was on fire 100 miles south of us) on CA I-5 the night before Thanksgiving 20 or so years back ... it was so obvious - large white unmarked truck, combat-style jeep-things front and back bristling with big antennas, full of scary dudes in fatigues and dark glasses - it was like something out of central casting - throw a McDonalds logo or something on the truck for heaven's sake
While sitting next to a nuke and not really knowing how safe it was was a bit scary the actions of the security dudes when people started getting out of their cars to stretch their legs was far more scary - they were actively menacing while trying not to give away why they were there or that the unmarked truck between their vehicles was in any way special (despite being stupidly obvious)
Sounds more like an aircraft/spacecraft part in transit. Or aircraft weapons. Regardless of the OP, nukes are small. They dont need big trucks. My money would be on a shipmemt of missles parts (rocket motors) or similar weaponry that you donr want shipped by air.
While sitting next to a nuke and not really knowing how safe it was was a bit scary the actions of the security dudes when people started getting out of their cars to stretch their legs was far more scary - they were actively menacing while trying not to give away why they were there or that the unmarked truck between their vehicles was in any way special (despite being stupidly obvious)