Weird x axis edge print

Experiencing weird print for square object. When the x axis was printing right to left back to front the edges were dish shaped. When printing left to right front to back the edges were straight. The front edges we're straight vertically but the back edges were dished shape vertically. When watching the x axis belt could see a twisting when direction was changed. Based on posts from others ordered bearings for the pulley and printed out an x axis tensioner. The bearings arrived yesterday. Installed the bearings on the pulley shaft installed the printed tensioner and pulley with the bearings. I did a test print saw no twisting in the belt print came out with straight edges. Wonder if a toothed pulley would totally eliminate any twisting?