ok a little update................ its fixed woohoo! mucho acceleration again 
had another look at the plugs leads and stuff tonight, took them out put them etc again all fine. went for a drive and its fixed will accelerate all the way to the limiter again. didn't reset the ecu as i was gonna do that tonight.
still have no idea as to why this happened :S maybe something had come loose and by removing/refitting it got pushed back in. again why it would only effect 3rd is beyond me :S
not gonna complain cos it'll break again
cheers for the help everyone
graeme 