Debug Zen Cart Upgrade or revert to old version

Our Zen Cart site was just moved onto new hosting and upgraded to 1.5.8. There are a lot of issues with the new install, and we need someone to go in and make it work at least as well as it did before the upgrade. If it cannot be made to work as well as the old version did, we will need to have the old version moved to the new hosting, and a new square module installed. You must have actual examples of Zen Cart work in order to be considered for this project.