first thing I would do is get the ecu fault code read, are there any members near by with a scan tool ?
also make sure the egr cheater is connected correctly, it will give an eml if wired wrong or a bad connection.
you could remove the egr cheater and reset the ecu, you will get an eml because the egr isn't there but not an ecu 'limp mode'
then if limp mode returns you can rule out the egr cheater, but that won't help matters as you still won't know the fault