What tranny do you have? Definitely go to a 3.73 or higher. The tow rating goes up with higher axle ratio number. Also don't run overdrive when towing. OD is the weak link, expecially on a light duty Mazda manual tranny. As for changing the axle ratio, my pinion went out on me and my mechanic said it would be cheaper and easier just to get a whole unit from the wrecking yard. I did and now about 15,000 mile later it is still performing flawlessly. I paid $250 for an open differential unit with 3.08 gears. I have a '95 F150 brochure I will try to look up the ratings tonight for you and post tomorrow (if I can remember).

INLINE SIX POWER! '95 F150 XL
300 Cubic Inches of Low RPM Truck Torque! And twin-I-beams too!
"Drive a stick young man! There'll be time for automatics when you're old and unable."