Reverse not functioning after replacing battery

@zacsevilla it is possible that when you disconnected the battery the Transmission Control Module (TCM) may have lost its Keep Alive Memory (KAM). Erasing that memory means the computer has forgotten the precise bite points of the clutches and the exact positions of the internal shift forks, which frequently results in a locked-out reverse gear and shuddering forward shifts.

Start of by performing a Static Idle Relearn which will force the transmission to find the baseline positions. Start the engine and let it reach normal operating temperature. With your foot firmly pressing the brake pedal, shift from Park down into Reverse, Neutral, Drive, and Low/Sport. Leave the shifter in each position for exactly 5 seconds before moving to the next. Shift back up to Park in the same 5-second intervals. Turn the key off, wait 30 seconds, and restart to see if Reverse engages.

Now, if that did not work you will most likely need to run a TCM Adaptive Relearn via OBDII You will need to connect a diagnostic interface (like an ELM327 adapter) and use software like FORScan to run the "TCM Adaptive Learning" service procedure. That maybe one of those tasks where a professional shop will come in handy. The adapter as well as the software may not be that easy to come by and/or use.