You know that TRex will not go down and up unless it is centered and that the center switch is closed. You've already reflowed the solder on the left right relay. Did you inspect the shaker motor board? Also, found these links with lots of info.
https://pinside.com/pinball/forum/topic/jp-trex-low-voltage-for-l-r-motor-everything-else-ok
https://www.marcospecialties.com/pinball-parts-blog/wp-content/uploads/2014/12/039A_SB.pdf
https://pinside.com/pinball/forum/topic/jurassic-park-club?tq=&tu=sataneatscheese