Cooling system exploded, but told it's a blown head gasket, what is going on here?

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1. Battery died, opened hood, reservoir top was off and reservoir full of rust-colored mud-like crud. Car never overheated. (Would start to get hot if idled for long period in Las Vegas summer sun, but NEVER overheated.) 2. Had a shop flush cooling system. They said it was "pretty bad." Agreed. 3. After that car began to overheat while driving, then within a few days the rust-colored "mud" was back. Inside of engine compartment sprayed with the stuff, and marks dripped all over driveway. If coolant/water added, car ran at optimum temp. 4. Car has full power, no missing, smooth idle, no odd sounds, no visible exhaust, no water in oil, no oil in water, but sometimes emitted odd, not sweet, burning smell from engine. Sometimes sounded odd upon starting, but if I shut off car then immediately restarted, no odd sound. (Almost like exhaust-leak sound.) 5. Returned to shop to have them re-flush system, thinking they hadn't done it right the first time due to return of crud and new overheating problem. 6. Shop informed me (after performing a "test") they were "100% positive" car had blown head gasket. Would not re-flush system-"didn't want to make it worse." 7. 160k mi on engine, out of work, $2500+ to repair, so I bought reputable liquid fix (www.rxauto.com) and took to another shop to prep car for adding repair stuff. They flushed system, were supposed to remove thermostat, add 100% water, add repair stuff, and I was then supposed to drive at highway speed for 20 mi to "set" stuff. If car overheated, instructions said cool off, add water, and idle for 5 min. Took to highway speed and car ran at optimum temp for first 17 miles, but on long uphill on homestretch temp gauge climbed up, got home, cooled it off, added water, idled as instructed. Next day, car overheated at 35mph within a few miles from home. No more rust-colored mud- just grayish water. The gray color from repair stuff. Was mud gone- or stuck and lurking in system? 8. Discovered reason for spray in eng. compartment-- reservoir fill tube that rubber tube slides onto was cracked, everyone missed that one. Installed new reservoir and radiator cap because old cap was worn. Test drove car and it ran at optimum temp running hard up and down local hill near home, maybe 10 miles total, however on the last pass uphill temp started to climb fast. Coasted home. The water was boiling away inside system--loudly. Let cool overnight. Added water. Drove car again, under 30mph, only 3 miles when overheating began in earnest. Added water later on, tried again. Overheating within 2-3 miles at slow speeds. 9. Instructed to put a new thermostat in, thinking car was running without thermostat b/c the shop charged me to remove thermostat. RXAuto tech said some cars need thermostat. Tech thought shop had left air in system and the car overheated b/c of air pocket. 10. Upon new thermostat install I discovered old thermostat still there, looking all worn out. Figured that must have been part of the problem, if not THE problem causing overheating. Installed new thermostat, checked all hoses, bolts, all good. Broke a nail. Added fresh water and rest of repair stuff as instructed. Idled with cap off for a few to get air out (someone else told me to do that.) 11. Test drove car: went 4-5 miles at 30-35 mph. Temp gauge just below normal mark. Car running great! Happy as can be! Short lived though. Got on freeway for 1.5 mi, 0-65 mph, free as a bird. At 60-65 just before exit ramp the damn temp gauge climbed so rapidly there was nothing I could do but coast up the offramp to the (dammit) red light and BOOM! from under hood, steam and liquid shooting out both sides of hood. No one next to me, no car or m/c--the one good thing. Sat steaming at stupid light FOREVER... (light green, slowly headed home, temp gauge rapidly falling lulling me into a sense of false comfort) defeatedly limped home with heater and fan full blast. Repair stuff everywhere on grill front q. panels, etc. Thought the reservoir had blown its top, but NO, not my car--- the top of the damn radiator blew off! Needless to say, I need a new one, but just FYI, the inside of the radiator now exposed is all rusty. 12. Even though this happened, as I limped 1/2 mi home, the car actually ran great- even better if I ignored the crap sprayed all over the outside of it. 13. So, what do you think of this? Is this a cooling system issue, a blown headgasket, or both? (Yes, I realize that NOW it has definitely BECOME a cooling system issue, but what caused this to begin with?) What was the mud? What's up with the blown h.g? (The shop who diagnosed it had nothing to gain at all by saying it.) What caused the top of the radiator to blow off? I installed the thermostat the right way--in the exact same position as the old one. The reservoir cap, which should have blown off seeing how it offered the path of least resistance, stayed on just fine, or is that normal when a radiator blows up? THANK YOU IN ADVANCE FOR ANY ADVICE YOU MAY HAVE!