94 1st gear only; typical ground issue?

On my 1994 GP 3.1, it has suddenly reverted to only running in first gear forward, when I was getting on the freeway. Prior to this, many 1st starts of the day, it would be difficult to get it to go into reverse, but it always did.

If it matters, the alternator died just before the main problem happened.

I read that this transmission has a problem where a transmission ground wire can cause similar problems, and in that case, I imagine it's a cheap fix. Is this likely?

Thx.

Any thoughts on this, please?