hi all, really starting to bug me now... when the car just starts and say for a good half hour runs like a dream, only when it gets hot starts juddering violently ,this starts around 4500/5000rpm but the longer i drive it the lower down the revs it gets.

just dont understand why this only happens when car is hot? anybody any ideas?? has had new fuel pump, spark plugs, fuel filter, maf sensor checked....