I installed the head upgrade last week and had issues. One of the issues was the spacers. The other issue for me was the new trex wouldn't catch the ball as frequently. I went thru all the alignment procedures both mechanically and software wise. After reinstalling and tinkering for hours, I put the original jaw on with the new head. That fixed all the issues. I'm not sure if the original jaw is a little longer?? When I have more time, I will try to dive deeper into the issue. However, I can hardly tell the jaw is different and plays and looks amazing.
Quoted from fooflighter:First thing I would check, with the power off, is that your trex isn't hitting the plastic guard right behind the head by moving it manually full left and right with the head in the neutral homed position, you can set this in the system test menu and then turn the power off when it's lined up
If your spacers aren't correct, the back of the plastic may hit either the trex or the crank shaft for the Stepper motor and limit the head travel.
You can use washers to space things properly or even cut the spacers if need be
Watch his install video at the beginning for correct placement
Another thing is the 3 screws used to connect the lower jaw... The stock factory ones are too long, either cut them to custom size with a Dremel and file and burring off (I did this) or get new ones, they poke through the bottom tongue plate otherwise and could cause ball interference
I have a little more experience with my TREX unfortunately, as my Stepper Motor Driver board got fried a month ago somehow, probably a short, and I got intimately familiar with the trex just doing all the checks and traces... So I've taken it apart and put it back on and off including the motor etc multiple times... My first instinct would be a mechanical issue in reassembly... It could be the jaw spring, alignment guides also, or a crooked optic jaw sensor...I would do a reinstall before tinkering with the tick settings