shifter rattles w/EZ installed

[EButler]

Can someone give me an idea what would cause the shifter on a 5 speed to shake and rattle after an EZ was installed. A buddy of mine wanted to test the difference of pulling his tractor with the ez and without. He tried the pull up a hill to test the difference. Without the ez he had to shift to 3rd, but with the ez he was able to remain in 4th. This is where the increased shaking of the shifter started just before and as he made it over the top. He's got about 85000 on the truck. What do you guys think?

 

[LSMITH]

What was the RPM when it was shaking?