Hey guys, I have a 5sp gearbox and in the last few days its decided to pop 5th gear back into neutral if I just ease off the gas a little bit. I'm also hearing an unusual whirring noise in 1st and 2nd when I'm moving off and I get a hint of the same noise when the stick is falling south out of 5th. I'd appreciate any suggestions...
My truck is a Toyota Hilux Surf SSR '91 which is just a rebadged 2nd gen 4runner

 

Do a search, this has been posted a few times.

It could be the plastic bushing at the base of your stick. Check it out.

 

96 Runner might be right on. My '89 truck had same problem..it was the stupid plastic bushing-thing (no noise, but it did pop out of gear). I think the trannys themselves are almost bomp-proof. 207K on mine...all stock. (Well, ok. One replacement clutch, but only because the throwout bearing was making noise).
Jim