Upgrading to the T5 and using the TA diff is going to give you all the cruising speed you want. I'm with you so far! But I question the need to "clip" to be able to drive 65 mph.
Aside from the "harsher ride" tweaking your straight axle and adding discs, sway bars, and decent shocks will get the job done. I've got close to 10K on my daily driver (webshots) straight axle truck and am a firm believer in the strength and durability it affords. My truck will cruise at 70 mph at 2000 rpms all day and aside from an additonal amount of feedback through the steering column, it handles as good as any of my late models. That semi that blasted by you at 85 mph pulling 80,000 pounds was running a straight axle. Just something to think about!!!
Dave
