Since he has COPs, the OP and anyone else with COPs may find a benefit from a computer tune. Although for the price of one, it may not make sense in the end. A good tune will advance the timing to the point where peak efficiency and power is created. The tune is just doing the same thing that advancing the distributor would do. Oh and a tune can also optimize shifts for better economy, too. It can change shift schedules and TCC lockups. This is what I did to my car, except tuned it for better performance, which also boosted economy as a side effect. Just do NOT get one of those pre-programmed chips/devices. They are a ripoff. I get my tunes done by Lonnie at
Blue Oval Chips but not sure if he does trucks. Alternitavely, you can get a dyno tune which will be the most expensive but give you the best results.
But putting the above expensive modification aside, proper tire pressure, tire alignment, and driving style can make a big difference in overall economy. Don't do jack rabbit takeoffs and you will improve economy in the city. Stick to the speed limits on the highway to improve economy on highway. Remember, the drag increases exponentially with speed.