I have just bought a 76 280z 2+2 the car runs fine exept every now and then it will start to slow down. the RPM's don't drop and it does not stall but just starts to slow down to a slow speed. anyone else have this problem

Strange......... Fuel??? but than again I always think it's a fuel delivery problem. test the fuel pressure.

If it's a manual transmission car, the only way for it to slow down without losing rpm is clutch slipping. Smoke and/or a nasty smell coming from the car when it happens would be a confirming sign.

If an automatic, I believe that bad clutches and/or a bad torque converter could allow the car to slow down without a change in rpm. Burnt transmission fluid would be a sign.

if the clutch was slipping i think i would see the RPMS spike up, but thats not the case

If you cruise down the highway in your top gear and then floorboard the accelerator pedal, does the engine RPM increase without the car going any faster? If so, then your clutch is slipping and would need rebuilding. Otherwise, there's no way for a car with a manual transmission (in gear) to slow down without the RPMs dropping.

When you say "start to" slow down, do you mean that you don't really lose speed (at least not enough to see on your speedometer), but you just momentarily lose a bit of power? If so, it could be any number of engine problems. It would be hard to be any more specific than that.

Wow, could it be a drag issue? Does the motor labor when this happens? If it were a clutch or converter issue you would definetly see high R's and feel the power go away. Check the brakes perhaps?