[Big Dave]

I feel your pain. My Impala is the same way.

Your options:

1. Don't drive it too much (under 7,000 miles/yr) and don't worry about it. If it has no monthly payments, that covers a lot of sins.

2. If you drive enough to motivate change, consiider trading it in, take you trade-in beating and buy a high MPG-car. Since you already have a high MPG car and still need to drive the truck I presume you have a need for it.

3. Become a hard-core, fangs-out, foaming at the mouth ecomodder.
What is killing you are:
a. The gas engine
b. The automatic transmission
c. The numerically high gear ratio
d. Lousy aerodynamics

Solutions:
A. Chuck the gas-pig motor and swap in a Cummins 4BT3.9 diesel
B. Chuck the frail, expensive automatic and swap in a T-56
The tranny swap kills two birds with one stone. You make a huge mechanical efficiency gain and the T-56 has a huge 0.5:1 overdrive which cures the problem with the gear ratio.
C. Chuck the flush top canopy and bribe Bondo to make you one of his superb Aero-Lids.

Do all that and you are in the high 20s to low 30s.

Low RR tires will help. Goodrich Long Trails are good in your size range.

Pidddle-around efforts yield piddle-around results.