i have 2 of these cars a 1996 and a 1999 which i just bought to swap all my mods from the 1996 plate and keep the newer one ..but after driving the 99 plate home it wont go past 90mph ? without a big struggle it seems its holding back on the horses!..any ideas please i dont think its the cats as iv had that problem with the 96 plate one and it dont fell the same as the problem on the 99 plate ....

Perhaps the newer car had not been used to being pushed beyond normal freeway speeds. As such its stored adaptation values has a hard time adjusting to your demands.
Hook up the car to a BMW GT1, check for faults, and clear DME
(engine) and (EGS) transmission adaptation values. Take careful note of fuel/air mixtures,oxygen sensor data, catalytic conversion, airflow meter data and possible ignition problems.
Would also be a good idea to check and change the spark plugs, possibly even the oxygen sensors.