1997 Ford Explorer Recently Purchased That Transmission Replaced Shortly Before

I have a recently purchased a 1997 Ford Explorer that the transmission was replaced shortly before I purchased it. It has not been showing any signs of problems either. My wife drove it to the store and when she came out the only gear that works is reverse. It has a 5.0 and a 4 speed automatic and is all wheel drive. I lost my job in November so funds are extremely limited. Where do I start to troubleshoot? Please help me with this