the symptoms you describe certainly do match a blocked DPF
if the ECU thinks the DPF is blocked then it won't allow full engine power so I'd suggest;
taking the car for a long drive where you can keep the engine rpm up over 2000 rpm for around 30 mins this will get plenty of heat into the system and get the system into re-gen mode
if that doesn't help then consider
or even removing it completely as you'll still pass MOT's fine without it, the key thing is to have the ECU re-programmed so its no longer looking for it
On cars where the DPF is removed then typically you get more power and more mpg as it restricts the exhaust even when new
also consider changing the fuel filter as if this partially blocked this too will reduce pressure.
If both of these are OK then also check the connections to the EGR valve, if either the vacuum pipe of electrical connection are damaged / corroded then the EGR can be on all time which certainly will hurt performance. Its also possible that its a fault with the EGR valve so its worth removing the valve and cleaning it out with brake cleaner, if it looks particularly clogged then replace it.
If this is OK then check the small vacuum lines to the turbo and its connected control solenoid on the bulkhead, any cracks or leaks can give turbo issues and its best to have the boost pressure measured actually measured with a boost gauge to check that the turbo is healthy and that the sensor is reading correctly
Also worth checking that the glow-plug relay is switching off as they can stick on and leave the glow plugs also on - on some cars this can force it into limp home
Also check all the high pressure hoses post turbo/s for any split hoses or cracked metal pipes, also check the ends of the intercooler as its not unheard of to pop the end caps off under high boost.