me 3.5 efi v8 has a bit of a strange fault pull away from a stand still and floor it it goes great through the gears and pulls like a train. Do 70mph down the motorway come to a small hill or bit of head wind and it dies just no power like the hill on the m6 by j16 stoke it goes down to 60mph even if i change down to 4th it wont pull. Any ideas