Ford GT Transmission Problems

Those symptoms do suggest a potential transmission issue. Error messages and shifting problems often point to hydraulic fluid issues. Have you checked the transmission fluid level and condition recently? Low or degraded fluid can cause these exact problems.

I haven't checked the fluid yet. If the fluid is the issue, would a simple replacement suffice, or could this indicate more extensive internal damage requiring a complete overhaul?

While a fluid replacement might temporarily help, the underlying issue could be more complex. Given the vehicle's age and mileage, consult a qualified technician. They can properly diagnose the root cause, whether it's a sensor malfunction, solenoid issue, or internal wear. Continuing to drive it as-is may cause more damage. A comprehensive diagnosis is crucial to avoid potentially costlier repairs.

I took the GT to a workshop, and they confirmed degraded fluid, plus some electrical issues. After a fluid replacement and fixing the undervoltage, the transmission is now performing optimally. Total repair cost was 240€.