Vauxhall Cavalier 1995 running problems???

hi, my car is running rough, when you drive the car hops and coughs and you have a total loss of power, the car has been serviced. oil, oil filter, engine flush, HT leads, air filter, fuel filter, spark plugs. but still the same problem. the problem seems to be worse when run under 1/3 of a tank. even with more fuel the car still does the coughing and jumping. when pulling away the car nearly stalls, having to use lots of revs and slow clutch. CAN ANYONE HELP ME??

Joseph Smith
February 2009