Engine Grinding Noise problems of the 2013 Chevrolet Equinox

I changed my oil when there was 5% left on the oil life gauge on 12/17/17. The used oil was black and thick and only 2. 5 qts came out. I put in 5 qts high mileage full synthetic oil and changed the filter. There had been no prior signs that anything had been going wrong and my usual mechanic hadn't told me that he saw anything wrong last oil change. The car started making rough noises, grinding and lurching the week of 1/15/18. I took it into the auto shop 1/22/18 since it started to sound like really rough grinding and started lurching hard while stopped. They told me that I had no oil in any part of the engine. They flushed the engine and did an oil change and said that they didn't see any leakage from anywhere. On 2/2/18, I was at a stop light, my car did a short jerk and made a short grinding sound, but then proceeded to drive fine. While stopped, I would start to smell an oily scent, but it would go away when I started driving again. Roughly 13 miles later, I was driving at approx. 70 mph when my rpm went from hovering above 2 to just above 3 and started deaccelerating. I didn't hear any gear shifting. I put on my hazards and took off cruise control and started for the shoulder of the high way (all without using my brake). The car jerked a few more times before the engine stalled completely. I parked it and turned off the car and went to check my oil level. After taking out the dip stick, I noticed smoke coming out of the opening. I wiped and replaced the dip stick and it came out clean, no oil. I moved to the rear of my vehicle and noticed fresh drips. I dropped down and looked under my car with a flashlight and saw oil everywhere. I got it towed to an auto shop and they informed me that the rear seal was busted and that I would need a whole new engine. My car has 114,465 miles on it.