The only reason I tend to lean away from tire balance is that the OP references acceleration and says it seems ok with no foot on the gas pedal. So it just sounds like its only upon acceleration rather than just always there at those speeds. To me a tire balance problem shouldn’t be affected by whether one is accelerating or not. Of course, further clarification would certainly help.
But the OP was also in the middle of a trip asking whether s/he should continue. I’d imagine that the deed is done - whatever it was and we may never know.