I have an 03 Mercury Sable 3.0 Duratech engine. The other day (the coldest day I drove my car since I bought it used) started to rumble/shake as I pulled out of my drive way. Once I got her on the highway, it was all fine. Today I drove about 30 miles to school, everything was fine. During lunch I was trying to accelerate and pass a guy on a bicycle when the car seemed to no accelerate at all, as if it loss 50% of its power. At this point I was thinking it had something to do with the transmission. Anyway when I finally get out of school and head back my 30 miles it was running good until I got on the on ramp to the highway. As I'm merging on there was another on ramp up ahead with someone else merging on, so I got over and started to accelerate. As I got up to 60mph the car started to shake and rumble violently, rpms shot all the way up then dropped to 3k rpm. The car accelerated in speed very very slowly and a light started to flash on the gauge cluster. I looked it up and it was an emissions light. Manual says if its blinking it may be a misfire code and to not accelerate heavily or else the cat might get screwed up. Afterward I drove it very calmly and took it easy. The car didn't have a problem until I started to get up and around 60mph or if I was going up hill. Has anyone ever have this happen to them? Or would anyone have any advice/pointers? Could it be as easy as dumping in some fuel injector cleaners into the gas? Could it actually be the transmission instead?? Thanks for any help in advance. Thank you! Please check back if you ask me a question because I'll respond shortly!