My folks in law have a late 80's 1st gen (Pre-Tacoma) pickup. I drove it 2 weeks ago and it was running fine, has about 160k miles on her. Last weekend they called me up to say that it will now only shift from 1st to 2nd and won't shift over to get into 3rd / 4th / 5th.

Any ideas what this might be?

 

I assume we are talking a manual?

If you are lucky and the shifter is very "floppy" its the shifter bushing and it cant pick up the slots for the 3/4 5 gears.

If you unlucky the trans is toast...

If its a 22RE motor, its a W56 series trans.

Last I checked $200 from a junkyard and $800 or so for a Marlin "reman".
A long day's work to swap in.

 

X2 on checking shifter bushing.

 

Caint find it, grind it.

X3 on the bushing. Hopefully it's that instead of your tranny. Try floatin the gears.