TD5 Irratic+intermittant misfire/hiccup under load

Please can someone give me some idea's of where to look next. I have a 2002 TD5 Auto which is my pride and joy, but i am beginning to loose patience. I am suffering from a irratic and intermittant misfire/hiccup under load at around 65mph when towing or loaded and have been doing so for nearly 2yrs on and off. I blew the torque convertor up last year in France while on holiday towing my caravan and suffered this misfire but eventually i lost all drive and had to be recovered back to the u.k. Having got the car back to my work, the gearbox was removed overhauled and a new toq conv was fitted. I still suffer with the hiccup. I have removed the turbo accuator to check for split diagphram (all o.k) and powered up the boost solenoid to make sure it works, the waste gate lever is as free as a bird. I have checked all the ecu connections for oil and cleaned them just in case, the cyl head wring loom was replaced 2 yrs ago when the injector seals were replaced. There are no leaks from the fuel press reg and the map sensor was supposedly replaced by a french landrover dealer last year in there attempt to cure my breakdown. I do work for an engine reconditioner but even my work mates are struggling.
Please can someone help????
Thanks Adrian

When you say hicup and misfire what is it doing? does it loose power completely? I am having a similar problem that's been ongoing for 2 years and it's looking a bit grim to say the least. Have a look here http://www.landyzone.co.uk/lz/f50/ongoing-power-cutting-out-problem-181732.html for the discussions about mine

It did it the other day, we were 7up and had been cruising at around 70mph for sometime but i felt as though the car was being held back slightly. We hit a very slight incline and the speed reduced to around 65mph and i had to accelerate slightly to keep at my current speed, it was then that we had a sudden misfire/hiccup and about 30 seconds later it did it again. After that it never did it again because we were back on the flat, but i was aware that the car still felt a little restricted. The car does very little mileage during the week as it is only used for local running around, like i say it only does it when loaded or towing and the engine is put under load at around 65.

It does sound similar to my symptoms, give the thread in the forst post a read. I have changed just about everything I can think of, and it's now looking like a cracked cylinder head. The best way to eliminate this is at the time of the fault. Once it starts doing it, pull over where it's safe, pop the bonnet and have a feel of the top radiator hose. You should be able to squeeze it. If it's solid it's not good!!

Had similar problem in previous motor, turned out to be a burnt exhaust valve not seating properly. Symptoms as you describe, misfiring under load - hills, accelerating etc but would rev fine under no load conditions.

Thinking about it, it could be a crack in the head along the fuel gallery. It can only be a small one that is being forced open under pressure when accelerating or under load. you would need to get the engine hot and then carry out a fuel pressure test by some how priming the fuel system without the engine running and seeing if you get a pressure drop.

Accy you may well have hat they call a trap door crack, but it is being held shut by pure coolant pressure, when the temp gets to a point where the crack is stronger than the coolant, the trap door is opened just long enough to cause the system to pressurise for a moment and send the temp guage up and then the trap door closes and you return to normal. it must be at this point when the misfire happens. Might be barking up the wrong tree but we have come across these kind of cracks before.

I'd re do the injector seals as cheap after that start considering more expensive options

a fault code and a live data check would be a good start

Injector seals were replaced early last year(had the typical poor start problem) cyl head wiring loom replaced year before.No fault codes.
I am going to use the live data recorder from work for a few days to see if that sheds any light.