2008 SR180 Injector and or Cat problems.

[acrmnsm]

My rav 4 has been declining in fuel economy for ages. 
I've never seen better than 33mpg.
However it is now down to 24mpg.
I do 15mins at 4000rpm on the motorway every now and again, to clear the Cat and it comes back up to 30ish.
When my wife has been using it, then I get puffs of grey/white smoke and a real stink of diesel, and now despite doing the CAT clearing thing it is getting worse and worse.
I took it in to main dealer in Exeter and they have said the injector feedback on two injectors is beyond the limit, 3rd close to the limit and 4th is high.
The recommended 4 new new injectors, we can play a game about guess the price. 

There is a local diesel specialist who has a great rep and has quoted much less, so I am planning to get them to diagnose it also. 

However nobody has mentioned the Cat,  given that when I clear it, I used to get some improvement, I wondered if there is any way this can be checked also?
EDIT- Also isn't there a 5th injector on the Cat? Sprays fuel on it to burn off the soot? That is the whole point of the Cat regen process at 4000rpm?

After my previous gearbox/dmf/clutch debacle I may as well have bought a different car as after this, the total now spent will be more than I paid for it... I do like it though. 

[acrmnsm]

A bit more news.

I took this to an independent injection specialist in Exeter, who were recommended to me by some main dealer types as a good alternative. 
They are unable to find a fault with their denso branded diagnostics, and have said they can't interrogate the injectors like toyota can.

If I take the Toyota diagnoses as correct, I thought to just get the independent to fit new injectors, but they have also said they cannot source the injectors right now.

That cliff is looking more and more tempting for my Rav 4...

Can anyone source injectors? Or shed any light on this?

[acrmnsm]

After various discussions with independents and Toyota, I got the main dealer to reduce their labour and paid 2300 to have 4 new injectors fitted. Part no's T23670-29015-84. The most expensive ones. In fact the cost from toyota is as good as any other reseller in the UK so I don't feel ripped off. 

Saw 38mpg average just now after a brief motorway stint, haven't seen that for ever and no smoke. Will report back on longer term averages.

However this might be my last toyota, after the gearbox and now this, I am thinking they legendary reliability isn't what it was. 
If I am still alive when this one dies I'll be going back to Honda.