Why is my 1533 massey running sluggish no power

Check fuel pressure, check for restriction in exhaust system.

OOhh well I guess you've learned that its allways a good idea to prefill your fuel filter when replacing it , see my tip for priming diesel trucks (works for tractors too) , well sounds as if now you got air bound injectors (air compresses -fuel doesnot ) you will need to loosten (not remove!!!) injector lines at head till they bubble as you crank engine over , sometimes a quick method ive used is to " spray" paint thinner (mineral sprits) into air intake as I crank , engine should sputter and eventually start as injectors take over fuel delivery

Air filter, fuel filter, clean the throttle body, especially the back of the plate and where it sits in the throttle.

If it runs good in park or at idle but is slugish when you try to accelerate it is likely a fuel issue. I would start with a new fuel filter. When you press on the gas you need more fuel pressure and if the pump cant get more through the clogged filter you will get that. If it runs bad even at idle it is likely a spark issue and needs new plugs and wires. I would give it a good tune up - oil change, spark plugs (platinum or iridium), plug wires, air filter, fuel filter, PCV Valve and see how she runs after that.

Having replaced the computer, best thing you could do now is a complete tune up-new spark plugs, wires, distributor cap, rotor, air and fuel filter. Change the oil and check all fluids. Have the computer scanned for trouble codes. Check if your catalytic converter is blocked or clogged-if bad, they will plug up and stop the car.

Did you have the fuel pressure checked and the fuel filter replaced ?

Generally, fuel problems cause an engine to lack power.
If the check engine light is on you should have it scanned for trouble codes. The fuel filter should be replaced every 30-50,000 miles and the air filter checked at every oil change.

diesel fuel run in the winter is a lighter grade fuel to help is from freezing, and hard starting in the winter. You mnay have to replace the aircleaner. And may have to replace the fuel filter located on to of the engine, just under the air cleaner housing. The diesel fuel now sold in the summer is a little thicker and having a hard time getting thru the old fuel filter.

try adding some lucas fuel treatment to your gas tank to clean those fuel injectors. sounds like you've done everything else i would suggest. hope this helps!!!