Originally Posted by au_Nightmare

Hmm I'd do a full (correct) retune. starting from idle.
http://www.mytsn.com/publ/publ.asp?pid=2242&exp=13&sn=2

I had a headache with my old D5 with a too low idle setting masked by the LSN needle (it sounded normal) that caused the slingshot effect you speak of. Got great run time though, over 20mins (yes HSN lean hehe).
Fuel was also an issue for me - I was running 18% oil, now running 11% oil and much happier.

BTW OD 77T should be fine, thats what I run & Recommend and it's a HOT plug not Med from the info I have.