I hear a rattling sound coming from the transmission whenever I'm going uphill and I'm pretty worried about it, what it could be?. I guess I MUST get my tranny checked. 1986 Mazda B2000 SE-5, reg cab, short bed.

Are you sure it's coming from your g/box? Detonation or "pinging", sounds like a rattle, but it comes from your engine when it is under load, like going up a hill!
It is usually an ignition timing issue which a mechanic can sort out.

Thank you so much, I'll have my mechanic to check that out, I just hope it's nothing serious. That transmission died on me a few years ago (6 years or so) and I guess I'm a little paranoid about it.