It actually goes of the PRNDL switch, if that is mis adjusted that can happen. Seeing as how the engine/trans was just out, might be a possibility. But since you didn't mess with the trans, probably unlikely.
well the interior is gutted ATM (Center console and all removed
just a driver seat so it might be something to do with the shifter
XPZ, Alum heads,150#, I/C, GEN V mps 3.0, N* TB CAI K&N fully built trans, JE pistons, L32 rods, Comp lifters, PRJ Fuel rails, 65# Injectors, elec pump, MSD wires, MSD coils, Alum control arms, AGX, vogtland, GMPP sway bars, rear trailing arms