No top end power

[emac]

just a couple of thoughts

first the xj of that vintage does not have a vacuum or mechanical advance, all done by engine management

yes i agree especially in an auto the pod style air cleaners will kill an otherwise healthy running motor, there only redeeming quality is looks and noise.

even though you have done an engine refresh, i would firstly stick a vacuum gauge on it ( google has plenty of instructions) and secondly do a compression test.

based on the outcome you then have something to work on

[layback40]

Petrol engines need 3 things;
Spark, if you loose it, it will just be cutting out.
Fuel, If your fuel pump is failing or you have a blockage, it will be gutless under load or at higher RPM. You say your fuel pressure is ok, is it at all rpm or just at idle?
Air, a restriction will make it gutless under load or at high RPM. Is your throttle body ok? Do you have failed baffles in your exhaust system?

Is it an issue under load as well or only at high RPM?

Is it misfiring at high RPM?

[eksjay]

Solenoids gone bad in the auto transmission?

Over the course of 28 years, this has happened twice in my 95xj. Easy fix.

[Classic Boy]

The 4.0L is not a torque monster, it is normally aspirated and only develops around 230ft/lbs at peak torque rpm. I have a WG 4.0 that is fine to drive in everyday usage but the car is around 2T then add a heavy trailer and it will struggle to maintain 100km/h on inclines it prefers 80-90 when towing on hills and often with the O/D switched off so the revs are closer to the peak torque rpm. Try and keep the revs around 2400rpm when hauling up hills as that is the peak torque rpm. Forget towing heavy loads with O/D engaged on inclines.

[Classic Boy]

As a post script the engine is no tyre frying monster but it is almost bulletproof reliable and it has a reasonable fuel consumption for a car of its weight.

[awg]

Late to the party

Make sure the lock up torque convertor is working

Consider to fit a transmission temp gauge

Consider to fit a manual vacuum gauge temporarily

800kg on an incline will heat up the transmission a lot

You should be able accelerate on a slight incline

Was the engine run-in with good practice

Do a compression test, that will be a big clue on power

Finally, a wheel dyno will give you real numbers

I have seen a rebuilt engine should put out 200hp at flywheel, 115 at rear wheels auto trans no lockup