If you're experiencing noticeable differences as you describe then I'd be looking at other things. For example, does the vehicle have a tune? Changing parameters from what's factory set can make a difference if those changes rely on input from a sensor that's now been effectively disabled and is giving the ECU a load of bull.
Well I had my MN serviced by Mitsubishi two days before I went on my trip to Sydney and they said it was running great.
It is only the third service it has ever had and they tested the EGR Valve & said it was working fine too (No EGR Delete connected of course). They then let the ECU relearn its parameters & it ran sweet as.
The only reason I retried the EGR Delete again was because I have had the same comments as yours from other sources so I thought that maybe it was actually my ute at fault, but I can assure you it aint.
The MN only has 45+,000 klm on the clock (as of Today) so it hasn't been driven to death or mistreated. And 80% of those KM's have been on Tar. Mitsubishi actually told me that I really look after it and that it was a credit to me.
Anyway, like I said it goes like a train without it, but soon as I plug in the EGR delete everything goes to Sh** within about 20 K's. The power drops a little, it rattles more & the amount of smoke &n soot it makes with it connected up is crazy. And it does use a little more diesel (Highway driving).
Who knows, maybe I got a dodgy one or something, but I do know for sure that there is absolutely nothing wrong with the MN on the Engine and driveline side of things.
But as I said the difference is like chalk & cheese so I am done with the EGR Delete & I won't be connecting it up again.
EDIT: I also have an iDrive fitted & I reckon they are not worth $250-$300 bucks either. Yes it makes the accelerator react quicker, but I am a big bloke & I had the old Lead foot to the floor mastered anyway. If you ask me I reckon the Triton goes good as it is...was. But you sure can have some fun in a muddy paddock with one of them there thingamajigs, dag nab it, so no I won't be taking it off.