SWR is a measurement of how the antenna performs, not the radio. Apparently the antenna on the shed is okay.
The truck antenna has a problem, not your radio. A new antenna that shows a high SWR probably isn't getting a proper ground, with lots of metal surface all around where it's mounted. The cable connectors are suspect if the coax has any mileage on it.
The standard coax connector is not weatherproof. Unless it is properly sealed against rainwater, it will soak up water and cause it to "wick" down the inside of the coax shield. That always raises the SWR.
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