2003 Mitsubishi L200 4x4 not working, engine management problem

Hey folks,

This one has me a bit stumped, any advice is greatly appreciated

I bought the above jeep a few months ago, since the day I got her she's had intermittent problems that are gradually starting to get on my wick,

Problem number one:

When driving the car she goes fine however if you put the engine under load, i.e., most notabley in fourth gear, if you are going up a hill etc and put the accelerator fully down within a quarter mile the emissions light comes on and kicks the car into safe mode, what's really annoying is I own snap on diagnostics equipment but when the light comes on and you plug it in its reading the full system but it's not storing error codes, something which shouldn't happen when the apparent fault is meant to be live? I changed the fuel filter almost immediately as I know from experience they have a tendancy to fail but that didn't work so I'm looking at overboost problems etc but it's a needle in a haystack without having at least some kind of pointer in the right direction

Problem number 2:

Four wheel drive fault, the car runs ok in 2 wheel drive however there's a roughness and vibration when accelerating, in 4wd high it doesn't seem to work at all, in 4wd low the car seems to work as described as it's on reduced speed and revs but the indicator light on the dash doesn't light up, the only time I see this wee green light is on start up when it flickers but won't stay on and the rear diff lock switch won't work either, I've checked the solenoid on the front diff and it appears to be working fine, the vacuum is there and it's not seized either, I have receipts from previous owner in regards to work carried out for a gearbox repair and a new clutch but I'm getting to the point I think I'll need to pull the box and see if it's been butchered inside and set to constant 2wd, I'm almost certain the vibration is down to a dodgy release bearing but in 10 years this is the first one that's got me questioning everything I know and it's my own bloody jeep

I'm looking to see if anyone else has come across these kinds of problems before I have to bite the bullet and pull the box which I'm resentful of doing given the current intermittent driving fault as it wouldn't be financially viable

My gut instinct is the receipts I have for clutch and box repair are either dodgy or as described the box has been butchered and not been sold as described