I am having the same issue. I have a 2018 Malibu LT that is having issues accelerating. It generally begins after the car warms up (roughly 10 miles). It accelerates very slowly until it hits 4000 rpms then runs fine until it shifts below 4000rpms. It hasnâ€™t ever had a check engine light on. I have had it to the dealer after proving the issue for 5 weeks and they can not figure out the problem. I would love to know if anyone has had this issue resolved and what it was.