So I changed my rear differential. A project for sure. Anxious to go for a ride and I find the car will not accelerate. In 1st gear it is fine, 2nd gear as well. In 3rd it begins to accelerate and just sort of cuts off. In 4th it will start to increase RPM and then just maintains the RPM it has. I can push my foot clearly to the floor and the engine will not increase RPM (yes...even downhill). In a few tests it kind of bucked and jerked,.... I stopped trying to force it.
I turned off traction control and this made no difference.

I was thinking TPS but that seems real coincidental, ... it was running fine before. An odd duck, but it is a 2017 with only 17000 miles on it, I don't suspect throttle body is dirty. I do have a tuner and it did this before I added tune as well as when I added tune and told the car of its new gear ratio. Made no difference.

Any ideas???

Brian