Battery went dead, we jumped start it. Now the Mileage and the PRND3L light will not go out

There is a communication problem between the instrument cluster and the main computer. This is an error code. There are so many possibilities it isn't funny. A loose connection, dirt, corrosion, damaged wire, module failure, etc. If the guages are all working, and the car runs, this is a good thing. When electronics fail to communicate, the vehicle can become unreliable, with stalling, failure to start, etc. being examples. I would check any wiring that may have been wiggled during the jump first, then have a diagnostic done at good garage. They may have a spare pcm to plug in to verify your units operation, these can run $100's, used units cheaper. Be careful with wiring, not to make things worse, and also be aware these systems control air bags and engine operation, as well as alarm, climate control, and so on- you don't need the air bags to deploy accidentally for example! Good luck to you.