2000 Disco, 104K, ran beautifully up until yesterday! Driving on I95, 70 mph and noticed a one time slight miss. Looked at temp gauge and it was a tad higher than normal. Kept driving, traffic was heavy. A few miles later I noticed temp gauge higher but not in red. decided to get off at next exit. Approaching exit temp got higher and truck started to miss and lose power. Looped around exit and temp went to red and truck lost power and cut off. Coasted to stop, popped bonnet saw coolant all over back of engine, with steam everywhere. Let vehicle cool, added fresh OAT and noticed that everything I put in was pouring out on ground. Looked for hose break etc. BUT to my horror, coolant was pouring out of the rear of the passenger side cylinder head. I felt aound and put my finger in a perfectly round hole, around the size of a quarter. Is this a freeze plug or something? What could have caused this catastrophic failure? Is my engine toast? Headgaskets are original. BTW, I have a 2003 4.6 with 106K. Is this going to happen again?