So I have a 1998 dodge ram 1500 5.2l 4x4 automatic, and I wanna swap gears. Right now both my front and rear diff are stock but my trucks lifted 4.5in and sitting on 315/75r16. And I want to swap gears for both power and mpg but mainly more power

 

Those are essentially 35" tires. (well, 34.5....) so, minimum 4.10 gears, 4.56 will give you better power, but, at the expense of highway fuel economy.

 

thanks now to find a place around me to get it regeared

 

Parts and labor, you are likely looking at 1600-2500 bucks, depending on parts markup, and labor rates. (that's both axles.)