I think in most older Fords, they don’t go into OD until 40-45 by design. That way your aren’t lugging the transmission. Also to help prevent hunting..... bouncing back an forth creates heat.... They also don’t lock the converter until you are in that range either...... personally I’d rather have it run a bit higher RPM and use a few cents more in fuel, than burn up a $2500 transmission trying to save a buck......
Now fast forward a few years, and the Ford transmissions want to get to the highest gear feesible as quickly as possible. My 2 6 speed autos, on light throttle shift up as quickly as possible. However, they will lock the converter in all 6 gears, and skip gears up and down if they need to.... on the other end, with your foot on the floor, they will shift at 7000 RPM.... (3.5 EB / 3.7 V-6).... I’ve never gotten past 2nd gear on the floor because you are normally 70+ at that point.....