Hello everyone!

I wondered if anyone on here could possibly help me?

I drive an Audi A3 51 plate, 1.9 TDI, it has done 150,000 miles now. It keeps loosing acceleration when i'm on a dual carriage way. Not all the time but it is happening a lot more now. It only seems to happen on a dual carriage way and only when i'm going 70/80 mph. The car will jolt and then I cannot gain any more speed other than 60 mph. It will not go over 2000/2500 revs. I have no lights coming on the dash, the mechanic I use has no idea! The air filter has been changed recently as we thought this might have been the problem but it hasn't seemed to have fixed it.

If anyone has any ideas or knows the problem that would be great!

Thanks in advance.