1989 F350 7.3
stock tires were 285
stock gearing 4.10
installing now 5.13
Before gearing would lose speed uphill at 55 in fourth but on the same hill would hold 65 mph fine under ambient temps of 90 degrees F pulling my trailer.
My goal ... like OP is to be able to hold 55 in fourth vs. any hill when pulling my rig.
On flat ground 5 gear is stupid tall... I have no business doing 85 mph in a 30 year old truck.
Fingers crossed 65mph (actual) is around 2500 rpm if in 5th and 4th @ 55mph is around 2800 rpm.