Are you saying that with the selector in "high range" all four wheels are turning at the same speed, but when in "low range" three of them are turning at a lower speed but one wheel is turning faster? How are you able to see that? Are you driving on gravel and three of the wheels are turning normally but one is visibly spinning and kicking up gravel?
The High/Low shift lever has two visible connections, with one going to each of the front and rear transaxles to make the gear change. If your problem was that both front wheels were turning at a different speed than both rears, then it could have been an issue with that connector, which may have been easy to fix (like the connection had come apart at the lever itself). But you’ve described that just one wheel of the two wheels on a single transaxle is spinning at a different speed. That suggests that something is broken inside the transaxle and it isn’t going to be a “easy fix” at all.