Mitsubishi Repair: 1996 Pajero, clogged catalytic converter, mitsubishi dealer

Question
We have a 1996 pajero it suddenly started missing under load. It was sent to the local mech who replace all the coils (only one was fautly the rest were changed as a precaution ) and it still missed It was then decided the values were leaking so both heads were reconditioned. It still missed. ( getting expensive now) We then took the car to the local Mitsubishi dealer who could not find the fault and said bad luck we can not help. So we have checked the computer o/p- no registered problems showing
we cleaned all the connections to the sensors with wd40
this stopped a idle hunting problem it also had but it will not idle without pulling on the hand accererator when cold . I treat this as a seperate problem.
So now when you  are crusing at 80k/hr and  lightly accelerate it will missing and shudder quite badly but if you accelerate hard it will pick up and go  with only an occassional miss.  Driving from a stop it missing untill it gets up to crusing speed driving at 100km/hr it will miss intermitantly. At idle or accelerating out of gear it runs ok so it hard to tell if any thing your look at is the problem as you have to be under load.
Where to now??

Answer
Greg,
You may have a clogged catalytic converter or air intake.  If you can get an inexpensive catalytic converter to replace your existing one, it may help.  Also check your air filter, fuel filter, and fuel pump.  Anything that blocks air flow or fuel flow can cause the problem you're describing.
Good luck!