2001 Jeep Cherokee stating issues?

It sounds like they didn't reinstall the neutral safety switch correctly. The switch is wired as an interlock to prevent the vehicle from starting unless it is in Park. A misalignment during installation or dirty contacts will cause that problem. It's silly to buy a new one because they are so expensive and can be repaired easily. Since your car was just in the shop for trans work, you can assume it is simply misaligned. There is an adjustment bolt to correct this. The NSS is located on the right side of the trans. you should be able to crawl under the vehicle and adjust it. The link below gives additional instructions.