Highway gear options/advice?

[Kell]

250 inline 6 with standard 3 OTT. My truck cruises comfortably at 55, anything above that is pushing it in terms of long term reliability I'm afraid. I would like to be able to drive on the highway instead of fearing it, I drive my truck a lot and this would allow me to drive it a whole lot more. I came up with 3 basic options?

1. I have 235/75/15 on there now, I would like to switch to taller tires anyway, but not sure if that will be a noticeable change? Any advice, or pics of taller tires (mine just look too small).

2. Switch the rear end out with an automatic? I've heard the rears are geared a little higher in an auto, this should bump it up some, but possibly make 1rst a little high?

3. Switch the transmission out, this is a pain, and finding a 3 speed with OD would be next to impossible around here. 4 speed floor shift loses some of the old school vibe I like about the truck, but I guess is an option. Have heard certain V6 S10 transmissions will hold up?

Any thoughts? Thanks