Vauxhall astravan 1.7, dti, 2001 model,

i have just had a new aromatic meter, rock a cover, oil cooler installed. the egr cleaned and exhaust cleaned. The van is fine in a morning but its as the day goes on it gradually gets slower and slower. The more mileage i do. in a morning it drives like normal. but when it goes, i cant get above 40/50 mph, smoke comes out back and a bit of a perfumey smell to it, like sutt. im to a point a might as well walk up hills so to speak. I couldnt even attempt the motorway when its bad.

iam at a loss please help asap, as its my work and family transport as luckily it has five seats

thanks ben