Ford Duratec he 1.8 hesitation and light stumbling when driving.

Hi,my Ford focus c-max 2005 petrol with 184000km has a fault/problem that seems to be worst when its hot out side like this warm summerst,its like it shuts down on power or a blockage..it will stumble and hesitates when going on the highway and now the last week the red engine light has shown on the cluster ..when i shut the engine of and start it again it is gone ..I have new plugs ,coils'il,filter,airfilter,T.map,EGR ,new throttle body(Ridex) new gasket after removing the intake original from Ford.,brake fluid,oil,new NGK oxygen sensor (before cat).My car drinks ca 1 liter oil on 1000km.I suspect the cat is clogged or bad but i have not yet taken it to a garage for OBD reading .Is there somebody in her that has knowledge on this Duratec engines that can give me som hints on what to check?PS:when giving half throttle it hesitates /stumble special on 2 gear but also on rest of the gears..when floring the gas pedal it will go fast if it doesn't hesitates..