12-14k load is maxed out or overloaded. The truck is rated for 16 and weighs 4K or a little more. The 235 is a good engine but not overly powerful.
Therefore not much need for faster gears, you'll never use them... Unless being foolish on a downhill.
I estimate the slow gears you have will be necessary.
Be sure brakes are in excellent shape, may consider a dual circuit master cylinder but otherwise original should be just fine. Try to keep total weight under 16k
