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. Anyone have an idea what could be wrong?