Smoke is unburned fuel. Either there's too much fuel or too little air.
Since someone messed about with the injection pump there's probably too
much fuel. But before tearing into the IP check the paper air filter
inside the engine's air cleaner and replace it if its very dirty.
Injection pumps aren't "weak"; the guy wasn't satisfied with the
diesel's off the line acceleration and tried to "goose" it by cranking
up the ALDA - too much, thus the smoke.
Transmission's fluid should be BETWEEN the dipstick's marks. Overfilling
will cause the fluid to become aerated and those little bubbles cause
the transmission to lose its internal pressures and slip. So check it
hot and remove any excess fluid.
You should know that this straight six is a fine engine but shouldn't be
overheated. Overheating can cause its head gasket to break and worse,
the aluminum head to crack. Be sure the radiator is in good shape and
don't charge long hills in hot weather - take it easy.