Misfire on v8 auto please help if poss

hi does anyone have any ideas about my disco's misfire.

history is went on hols came back got in car it was misfiring badly.
into the garage it went and diagnosed with needing new plugs and leads. had these done and still it was misfiring. had one coil pack changed and all seems to be well until it hits 40 miles per hour seems to be on the last gear change then the misfire starts again.

OH seems to think we should have other coil pack changed and garage did recommend that both are normally done at same time. but hey plugs were £ 8 each and was 3 days before xmas.

mechanic seems sure he got right side for the coil pack as it wasnt firing on drivers side. and he brought it back saying all was well. obviously we gotta go back to garage but just thought i would ask on here if anyone got any ideas.

its v8 auto 4 litre. x reg

ps there is no engine management light on at all.

many thanks for reading this

Swap over the packs and see if the missfire moves.

great idea will pass that onto OH, many thanks

Torque converter flex plate is very bad for cracking .That problem can causing a misfire .