Line Mode job - using a light grey screened box. Looks good in Designer. Looks dotty and grainy when printed. I don't get this problem when coding a DBM job.

Is there a setting on the controller I need to change when using JDT's?

I don't see any reason to this. What do you mean by "light grey screened box" ? What is your code for this ?

2101 2517 369 2437 LMED DRAWB % BOTTOM BOX

and this one

2075 1596 397 9 LMED DRAWB % AMOUNT DUE BOX
2075 1694 397 95 LMED DRAWB % AMOUNT DUE BOX
1689 1014 399 100 LMED_S1 DRAWB % AMOUNT DUE BOX

very pixely. not a smooth grey.

There is absolutely no reason why this should be different in a JDT versus a DBM. The same code is executed in both cases.

You may need some setting on the controller to apply a different screen to gray areas but this as nothing to do with JDT or DBM.