have an 98 gmc 6.5 beches out black smoke when you take foot of excelorator and revs up diesel place says it could be injection pump is there something else it could be

 

any codes? could also be the injector drive module

 

Check air filter , check for exhaust and cross over pipe leaks chack vacuum system and wastgate

Most of the time bad IP will trow codes PMD won't 99% time could also be bad injectors how many miles on injectors and IP

If you still have stock exhaust it most like it clog and that lone make smoke black