1994 B3000 5th gear problem

[fisherbear]

hello all from a Newbie...
I've had my 1994 Mazda B3000 for over 6 years without any major provlems... I really like it and want to keep it as long as I can... I noticed a few days ago that it made a weird hi pitch noise when I put it into 5th gear and tonight noticed why.... going from 1-2, 2-3, 3-4 gears no problem... rpms go up and it speeds up as normal... when I shift into 5th it'll speed up but, the tachometer will stay at the same rpm and NOT go up with the speed... it'll stay at the same rpm as when I press in clutch from 4th gear and just stay there... sometimes it's 1,800 rpm... sometimes it's 1,200 rpm... I don't want to burn up the gear... has anyone here dealt with this or know what may cause it?
is it something internal? any help is greatly appreciated... thanks...

also, does anyone know what kind of tranny is in my truck and how much roughly to fix/replace... thanks...

 

[leethesme]

Type of Transmission

I believe your transmission is probably the M50D-R1...I recently bought a 1994 B3000 X-cab SE 5-Speed and the way to tell is by the TRANS Code on the door sticker...if the code is M then you have that one. I don't believe there are any others for this model year with the 3.0L.