Why won't my 1987 mustang gt with an (aod) transmission shift into 4 th gear when using the (od) on my shifter when in (D) it shifts up to 3erd?

If your 1987 Mustang GT with an AOD transmission won't shift into 4th gear when using the OD setting, it could be due to several reasons. Common issues include low Transmission Fluid, a faulty throttle position sensor, or a malfunctioning governor that controls the shifting points. Additionally, the AOD may be in "limp" mode due to a detected issue, preventing it from shifting into overdrive. It's best to check the fluid levels and consider having the transmission diagnosed by a professional.