More than just a coolant flush..

[scotts62]

Ok i have a question.. i have looked around in the search but didnt really find what i was looking for. I was helping my dad out on his '98 Bravada earlier because its not heating up like it should and we flushed it out really good a few weeks ago and got a bunch of nasty out of it and figured all was good but its back to acting up again, i let it warm up and pulled the cap and noticed that the flow of the coolant wasnt very good and it wasnt pouring out of the cores like it should when its at its best. Looks to me like the people before didnt take care of it and let some rust and gunk build up in there and now its stopping it up.. So my question is, is if there is some stuff out there that will give it a good flushing and help open it all back up or if i should just buy a new radiator and heater core and go about it that way?

Thanks,