orange coolant?

[Boog]

My recently purchased 2000 GMC is my first to come with the ol orange coolant in it. I guess it's dexcool. I noticed the coolant recovery tank was stained inside making it hard to see the coolant level but didn't give much thought to that buildup elsewhere in the system. The truck runs normal temps just fine but now that the mornings are a bit cooler I sometimes need a warm defroster. Not even close. Luke warm air with temp knob on full hot. I first thought it had good coolant flow in and out of the heater core but after starting it cold today and monitoring the heater hoses I found hot water going to the core but very little coming out the return line. I popped both hoses off and first backflushed the core and large chunks of brown mudlike substance came out with some small flat hard particles in it. I reversed the flush several times until all that came out was clear water. Hooked the hoses back up and I have good hot air now.
Knowing there is that junk buildup in the system do I dare to use a brand name flush to remove all I can and go back with the conventional green coolant?
Many years ago I used a two part Dupont cooling system flush. It got the inside looking like new but the next day the water pump went out. I know, it was just time for it to go out anyway. Now with this newer one I don't want to go down that road.
Any suggestions on whether to flush and go back green or flush and go back orange or top it off and leave it be? Thanks.