getting big vibration after shifting into higher gears.

The clutch is slipping, fairly indicative of a worn clutch that is due for replacement.

wow! thanx for the prompt attention..
In fact, I ve just replaced the pressure plate & clutch plate

Did you get the flywheel machined?

Nop!! how does it go.

The fly wheel will have hot spots on it, these look like bluish marks on the surface and possibly there is also localized spot cracking, these hot spots cause the different coefficient of friction, in layman's terms it causes the clutch to grab or shudder under load during take up, the only answer is to get the box out and get the flywheel machined, this should be done each time the clutch is replaced, the chances of a faulty pressure plate are quite remote, as you have not had the fly wheel done, i am sure that this is the problem.

Ghee!! thanx MH, I will try to talk that way to my mechanic. By the way, apart from that reason is there any other likely cause!!

only a faulty new clutch, but i doubt it.

Like the whole set; pressure & clutch plates and release bearing?

Normally a clutch plate, if you look at a clutch plate there is a set of wave springs between the drive disc's, this is for impact shock loading, in the hub (center of disc ) around the spline are large springs, these are the torsional cushion springs, if these are faulty this will give a similar symptom, but i wound put money on the flywheel not being machined as the problem, this should be done at each clutch change, not doing so is just asking for problems, and guess what........