518 short shifts and no od

You might have to change the position of the cable so it pulls from the idle position to wot.
The throw on the carb or t.v lever needs to be adjusted so when you step on the throttle the cable moves from idle to wot.This needs to be done first before you can adjust the line pressure properly.
Most of the time the problem is on the carb linkage,might have to move it closer to the center shaft of the carb for less pull on the cable,if it is to far to the bottom it will pull the t.v to quick binding the cable.
Try pulling the cable out and clamp it to raise the line pressure to see if it changes,leave it disconnected from the carb,the farther you pull it the later the shift,like I said before if this makes no difference it is in the transmission.