Vauxhall Vectra sudden loss of power for split second now and again

car has developed problem when driving along she will loose all revs for a few seconds and return again fine. egr valve, inlet mainifold, swril aculators and fuel filter have all been replaced by vauxhall and the diagonis says shes all good. ive tryed two bottles of fuel flush but its still playing about. she is still a lively car and pulls 100% rite up the revs in every gear. my heart is broke now as she is doing it more often and espically when pulling out at junctions. also i never seem to be away from vauxhall with my wages.