OD out in 93 bird

If it operates normally until it shifts to 4th (OD) where it seems to go into nuetral, then your problem is likely a failed band. This is a common failure. The only repair is usually an overhaul because the trans has to come out and the front section removed. You are not far from complete overhaul at that point and, it only makes sense to finish the job once you get that far. You will already have paid for 98% of the time and labor. You may want to look at a used trans but, you will probably not get a lot further with that. An overhaul that includes a few updates, a couple of modifications and a correctly installed shift kit will prove to be the way to go if you intend to keep the car for any length of time. These changes are usually minor expenses if done at overhaul. If you are concerned about future band failures, you can have a wider heavy duty one installed for only a couple dollars more but, be prepared to know when it upshifts. I don't find the firm shift objectionable but, many do if they like the soft shifts. A good trans tech should be aware of all of the usual mods to improve reliability and performance.