Weird mechanical problem with my truck

[ROcHE]

I'm the owner of a '93 Mazda B2200 which as been running flawlessly for the past years. Since a couple of days, when I put the tranny in 1st, 2nd, 4th, fifth or reverse without releasing the clutch, my rpm goes from 750rpm to 500rpm. If I move the shifter to neutral it goes back to normal idle rpm. I don't think the clutch is defective since the truck is not moving or even trying to move when I put the first gear on. It's some kind of intermittent too. I can ride for 10-15 minutes without problems, then the problem come back, goes away, come back, etc. Anyone have a clue ?? Thanks.

 

[notfred]

Clutch or clutch cable.

 

[d33pt]

yeah how long has it been since you replaced the clutch? i say pretty soon it will start slipping...

 

[ROcHE]

The truck have 172000 KM. Original clutch. I though that a dying clutch would have some kind of slipped or the truck would have moved a little bit even when fully pressed ?