Hi

I have a dax rush with a 2wd sierra cosworth engine runing about 300bhp. Just had a service new plugs, leads, cam belt etc etc. When nailing the throttle pulls like a train and back end snakes all over the place and pulls to 5000revs then stutters coughs chokes and misses change gear and away we go agian any ideas what would cause this only seems to happen at 5000 revs ticks over fine and no missing or stuttering before 5k.

any help ?????????????????