my 2004 6.0 has lost some power and the head gasket is leaking into the coolant. How long can i continue to drive the truck before too much damage is done to the engine?

 

The longer you drive it, the more it will hurt it. If possible, do not drive it at all.

 

I depends on what kind of failure you have. I ran 4-5 days and 1500 miles on mine because I was on the road and had a schedule I had to keep. I didn't have any contamination and was only losing about half of the coolant in my degas bottle every other fill up. Monitored my temps close and babied it and I didn't have any other damage. Heads were fine, no overheating, just a HG repair.

 

Oil in the coolant?

 

yes, there is oil in the coolant

 

If there's oil in the coolant you have a ruptured oil cooler,and you should stop driving immediately!

 

I have been loosing coolant slowly , notice a couple of weeks ago my horse power has been reduced

 

Losing coolant is one thing, but if you have a contamination you should really stop driving it.

 

It's common for shop to diag all manner af 6.0 issues as being headgaskets. Of course with your coolant loss they may very well have failed also but, oil in the coolant is a failed oil cooler. It's very possible (and common) that you need both the oil and EGR coolers, much less work and expense than headgaskets.

 

forgot to mentioned but oil is leaking out regularly, not sure where, but it is on the top of the engine

 

Lots of options for an oil leak up top, oil pressure sending unit, cracked oil cooler cover or just a leaking seal. All of that is coming apart during repairs anyway.

I'd pull the EGR valve and look for coolant in the intake manifold that would indicate the EGR cooler is leaking.