Audi 80 B4 jerks to long distance

Hello, my Audi 80 B4 2.0E, built in 92 with 85 kw, automatic and 175,000 km, shows an unpleasant phenomenon lately. Always after about 270 – 280 kilometers driven he starts to jerk strongly and takes only sporadic gas. That has always happened up to now in or after construction sites, i.e. at 60 – 80 km/h. He then jerks down to 20 km/h, then he takes gas again up to 100 km/h and so the rest of the route goes. In short distance traffic he runs however I was now in an Audi workshop, which unfortunately could not find the error. The diagnosis was: Ignition coil tested – perfect tank is made of plastic – so no rust injection system ok Lamda control and temperature sensor ok throttle flaps ok spark plugs ok Does any of you have another tip where to look further?