I'll just pass on what was suggested to me by Pro's when my 159 2.4 started juddering at about 2k revs/ 80 mph. One suggested that the ECU was sensing clutch slip and therefore cutting power, another took a guess at swirl flaps leaking/not working properly. Maybe your engine didn't have swirl flaps, but if you've had a remap, maybe your clutch is on it's way. Have you tried booting it out of a roundabout in too high a gear to see if it slips?
Hope you get it sorted, pretty annoying ey. My 159 is having gearbox overhaul, clutch, inert cv joints, it'll be great if it sorts out my juddering.
GT 3.2 V6 - Q2, KONI FSD & EIBACH PROKIT, GTA REMAP, MICHELLIN PS3's, BMC CDA
159 SW 2.4JTDM TI - ALFATUNED, WIZARD BACK BOXES, KW V3 COILOVERS, NOKIAN WR A3/MICHELLIN PS3, PCA DYNAMICS ALIGNMENT.