Hilux Surf Ln130 power problem

[Naysayer]

 have a 1990 Hilux Surf 2.4 lt with a 3 lt head already done and replaced the glow plugs  just to get that out of the way. She runs and starts good in the shop but when you take her out on to the road she starts to lose power and blows black smoke. NO idea as to why or where to start looking for the problem with out spending a lot of time and money. So I am looking for some help from a larger pool of people that may have has this issue and can point us in the right direction.

Thanks