I had a GMC truck for a little while that spun a main bearing. Regarding the original post, IT HAD BEEN NEGLECTED. I got it cheap, it was beat up, and the oil pressure was low. Despite that, it ran perfectly for several, several thousands of miles since I had acquired it. Every morning, I would let it warm up at idle, then drive it pretty easily. I took it on the highway and hauled with it often. Then one morning I was in a hurry and only let it idle for a couple minutes and drove it harder than usual. Surely enough, accelerating quickly up the bridge, I began to hear the rattle! I knew it would happen eventually, but it made me mad to think that I could have prevented it a while longer. I probably drove it another 1000 or 1500 miles with the spun bearing, highway and hauling haha.