I have a 1999 f550 super duty with a 7.3 in it my main concern is the excesive fuel use and the black smoke under a load what can be done for this

Black smoke is usually a signal that there's too much fuel, not enough air, or injector pump timing is off. One of the most common causes is an air inlet restriction. The cause may be a dirty air filter, a collapsed intake hose, or an exhaust restriction.

Synthetics all around will help gas mileage and help minimize black smoke:

. Full synthetic heavy duty diesel engine oil.

. Full synthetic automatic transmission fluid in the transmission and power steering system.

. Synthetic gear oil in the differential.