Ford Expedition 04 Engine: 5.4 Triton 2v Trans : 4r70W 4x4 250,700 miles

I bought this vehicle used for $1000 in May. Previous owner said it is missing 3rd gear and OD, the vehicle only shifts into 2nd with OD off. The transmission fluid level has remained the same since I’ve had it and appears somewhat fresh, and I am wondering if this could be an electrical issue or if I might as well get a rebuild/reman. I would appreciate some advice, Thank you.