Just putting it out there... An OD transmission swap like the t5 will give you comfortable cruising and 5 usable forward gears. The t5 works best with the 3.90 rear end.
What size tires are you running? Changing to a larger diameter tire can have the same effect as changing the gears to 3.38. For example...
27 inch tires with a 3.38 ratio will act a lot like 31 inch tires with a 3.90 ratio. If you have 27 inch tires on your truck and change to a taller 31 inch tire, you will have effectively changed your gearing by about the same amount, without actually having to tear anything apart.
