If you use trainstore, unstore everything then reinstall the route.
You might want to download the latest Tsection.dat file from UKTrainSim since most routes require the latest version (registration required)
Also, on the 'options' tab on the MSTS menu try turning down some of your graphics settings - in particular turn off 'distant mountains' since that uses up lots of RAM.
This section of the forum is pretty quiet so try asking the same question on the UKTrainSim forums (go to
www.uktrainsim.com and click on 'Forums') where far more people will be able to answer your question.
Best of luck,
Tom