1997 E320 2900rpm stumbling

[justme300e]

Hello guys! This w210 is my daily driver. It has 257,000 miles on it. I've changed coil packs and associated components, spark plugs, crankshaft position sensor, cam position sensor.
The pressure remains at 55psi through out rpm range.
The engine will not go above 2900 rpm without throwing a fit. I can have in park, Rev the engine and it will stumble at 2900rpm and above. I can only drive 75mph ,no faster. If I try to do 80 mph,it will stumble until I get back to 75 mph. Drives perfect up to 75mph though,will cruise control all day at that speed. I could really use some advice, because if I buy another car ,my wife will want it. Thanks for your time!