1998 Disco 3.9 EFi dies when putting in gear

This is my first post. Be gentle with me!!

Hopefully someone will be able to offer some assistance. I've tried to include as much info as possible.

When cold seems to start fine. Can drive but will stall when gets hot.

When hot starting is difficult. Always cranks but will take ages to fire up.

When started will idle at 6-700 but as soon as put into drive or reverse will stall immediately. A bit of throttle will prevent a stall but after a few seconds it will go lumpy and then stall.

Have replaced cap and rotor. Have temporarily swapped out AFM and ECU with no effect. Seem to have good sparks.

Had a temperamental fuel pump connection and so swapped out fuel pump. Seemed to run much much smoother while running but (as above) dies when it gets hot.

Another bit of info that I'm hoping is not relevant. Had a faulty brake pedal switch that was diagnosed by removing relay and short circuiting diag port. Switch replaced, fault cleared, ABS warning gone and brake lights working fine. am wondering whether I could have refitted relays (I think I had more than one out) incorrectly. Is that even possible? If so, could relay issue be causing the stalling problem?

Everything seems to be working properly but can't get a handleon the stalling problem.

Any thoughts or recommendations gratefully received.

Thanks

Kevan

Starting with the simplist, the crankcase breather and hose to the plenum could nead a clean same with the "stepper motor" idle control valve, it could be faulty also the coolent temp sensor could be faulty that's the one that sends info to the enginges ecu not the dash temp gauge,
I've found that a bottle of Redex or similar in the fuel tank sorts a few running problems out.

If you have had a poke around the fuel system you may have disturbed something else, not saying it is the problem but symptoms sound similar to a problem I had on a 3.5, turned out that the previous owner changed everything he could think of and had actually fixed the problem (immobiliser fault) but when it had a new pressure reg fitted the vac pipe split. So he created a new problem with similar symptoms to yours, not had a 3.9 so dont know if they have the same set up but maybe worth a look.

HTH