Going from 10 to 14 is a 40% increase. That's really tough, and quite honestly unrealistic. Unless something is really out of whack right now like ignition, fuel system, or plugged cats, all the help in the world is probably not going to get you a 40% increase in mileage.
Skinny tires will help reduce rolling resistance. Their lighter weight will also help a tiny bit in town since you won't be using as much right foot to get the same acceleration.
A good tune up will get it back to its original glory or close to it.
Don't fall for gimmicks like tuning chips or fuel catalysts. One thing that might help is a higher temp thermostat. If you don't already have one, swap to a 195* stat. The engine will lose a little power, but it will also inject less fuel.
You might pick up an MPG or two when your area switches back to "summer" fuel if you live in a cooler climate. Winter blended fuels contain up to 15% ethanol which hurts mileage
Find out your rear axle ratio. Sometimes trucks (especially 3/4 ton and up) are geared to work/tow. You might pick up a little by switching from your 4.10s to 3.73s or similar. If you already have 3.73s I wouldn't neuter it with 3.42s or anything steeper.
Figure out your yearly fuel cost at your current mileage, add in all the modifications you would have to do to get a few more MPG, add the trade-in value of your current truck, then price out a same-year cummins. My guess is that they'll be similar in total investment, but the cummins truck will give you 20-25 mpg all the time. That's double what you're getting now, plus you'll double your torque, have much higher resale value, and an engine that is designed to go 300k miles and more without any major service. Basically what I'm saying is, you'll invest the same, but the higher mileage of the diesel will start paying you back compared to keeping your existing truck.
Just a thought.