Hmm str8 6 go to 20” and the op’s only to about 30” . Something doesn’t add up. I would pull the pins in the top of the lift links where they attach to the rockshaft arms, check and make sure the pivot balls in the top of lift links are free to move. Lubricate them well and free them up if there corroded or painted stuck. I would also check the pivot balls in the arms where they attach to axle, all 4 of these pivot balls need to be completely free to swivel. If any of them are corroded or painted stuck it will cause your issue.