To start with I would replace the fuel and air filter's and run a good inj cleaner at double strength through the tank, I would also change petrol station's and run the tank down low before dropping in the inj cleaner with some fresh fuel, this will mix the two nicely and you should get a good clense, you might also want to check the clutch out, if it's sticking and you aren't getting full friction this could indicate the clutch is on the way out, a test is to keep the handbrake on, 1st gear and feel for the bite point, if it's high up the chances are the clutch is worn out, if it bites positive and near halfway up it's fine, hth.

I would get a new egr valve myself, even though it's seemed fine for 3 years it will still be coked up, and a blockage can spell running troubles


Cheapish diagnostic machine is an Autel one, you get them from eBay, just under or around £100 or £250 buys the Rosstech lead and software.