You are not alone on this one. I also have a '17 350 and occasionally will be unable to push the shifter into reverse. I lift the reverse collar and push into the reverse position, but it just feels like there is a wall in the way and I can't get it into gear. The only way I have found to get around this is to put it in first and move the car an inch or two in gear (luckily i usually have room in front of the car to do this), then after that I can successfully engage the rear gear. It hasn't happened enough to piss me off yet, and since I can get around it by engaging first gear, I haven't bothered looking into it. So if anyone else knows why it happens, and/or how to fix it, I'm all ears.