Unfortunately it's not so much the three-on-the-tree, it's the manual transmission. Yes, topping out at slower speeds, basically anything under 85-90 in Texas, you're getting run over. About 99.9999999999% have automatics in their vehicles nowadays, and when you take off, then let off to upshift and the vehicle slows down, then speeds up, then slows down again on the next upshift, they seem to take it as a personal attack on them and develop road rage. Happens to me every time I drive a manual transmission vehicle and it doesn't matter which city or state I drive in, people are just impatient like that now. If you're just wanting to go really fast, yes, you need overdrive or better rear gears to allow faster highway speeds. I wouldn't recommend going faster until you install a front sway bar. I know you want to lower the truck, but that won't make it handle better without minimizing body roll.