i recently whipped my 3.5 engine out to replace rear main, clutch, fork and release bearing. didnt touch anything on the engine leads wise etc but since ive put it back in it seems to have developed a missfire when in say 4th gear at 1500 rpm it judders and missfires then spitts flames out of the exhaust like its over fueling. ive put new leads and plugs in since but still does it. the coil is semi new so just have run out of ideas. anyone help