Here's how these things work, and WHY you turn the 3-4 shift lever is DOWN because that reverses the shift mechanism operation.

When you put the lever in "3rd" position, the reversed lever actually puts the transmission in the "old" "4th" gear (straight through) position, and when you put the lever in 4th, the reversed linkage actually puts the transmission in the old "3rd" gear position, which now is comprised of the overdrive ratio.

A little clue for ya. If you have any hard pulling or trailer towing, the "new" 3rd gear--the straight through gear--is much much stronger than the OD 4th gear.