If your going for mostly highway driving, think twice about going mt/s, your gonna die with the road noise, on the work truck i drive we have km2's on it, and they are loud, i can hear them over the diesel, and the 7.3 is kinda loud.
Also once a set of mt/s start to wear, they'll just start wearing faster, and faster, especially if you get cheapo ones.

Go for a set of 33 at/s, running 4.10s with that you should be fine. But it wont be as responsive. A 3 in body and 3 in spindle will be fine, no need for a 1.5in leveling kit.

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2001 Mazda B-3000 CabPlus "FX2 Off Road"| 3.0 | 5 SPD | 3 In Spindle Lift | Belltech Shackles | UltraGauge |Alpine Head / 10" Kicker Setup | Air Box Mod | Add-A-Leaf| Thrush Welded B4 Rear Wheel | Kobalt Box | Cobra 19 DX IV | Custom PA Speaker | Front/Rear Tow Receiver | 2X Aux Lights | Hideaway Strobes | Back Rack Safety Rack | Amber LED Strobes | Blue LED Strobes | 265/75/R16 General Grabber AT2's