1988 Ranger (2.9) A4ld slipping in drive and overdrive.
Does this usually require a rebuild/replace or could the
computer, or an electronic part be a possibility? How about
vacuum? Thanks for any help.

Pull the dip stick and if if the fluid has a burnt smell it needs a rebuild.

I did change the filter. The fluid I drained did not smell burnt.

I would get a couple of estimates at some independent transmission shops I think the right person could fix it but most will quote a complete rebuild.

Thanks for your replies. I did have this transmission rebuilt
about 40,000 miles ago. From what I have read online the
a4ld does have problems. What's a good manual transmission
that will bolt up to the 2.9 engine if I decide to do a swap?