I have just had this problem with mine and fixed it! Put it in 4th doing 40mph and put you're foot down... does it lurch then?
I found my leads and coil pack were the 12 year old originals and had gone wrong! But as you have replaced your coil pack it could be a lead...
Also, look behind the inlet manifold, there should be a T-shaped rubber hose, has it flattened at all, and when you turn the engine off is there a hissing noise for a second or so?
- Greenslider likes this