DPF under car , in the middle of exhaust with 8 bolts and one sensor
without DPF and with remap 2.5 will be in completely different stage
if DPF is really good , keep it for future if u really think to hold that car for over year or more,which i dont think will happen :hehe!:
but u will need to fit in some custom pipe or another DPF case without internals to keep exhaust in original look

do diagnostics for glow plugs , if it says that any of them gone , take out manifold and check all of them with multimeter . if even one or two are gone ,replace all of them . if diagnostics says that few gone but all ok ,replace relay as its faulty for showing faulty plugs even they are ok
fit 12 new inlet manifold gaskets , remove swirl flaps as early or later they do fail and oil leak threw them as well . and U will forget about these problems forever

If U gonna do remap anyway ,u will get that torque back even without flaps