1999 Chevrolet Silverado 1500 LS Extended Cab Pickup 3-Door 5.3L

1999 Chevy Silverado LS Extended Cab with 5.3l V8. Have over $6000 in receipts for work done within past few years. Need something i can get better gas mileage in. Just drove down to FL from WI towing a honda civic with no issues. Has AEM Cold Air Intake, edman Headers, ual Magnaflow Exhaust. Aftermarket rims, ood tires. Has minor bubbling on rear wheel wells but nothing major. Truck has treated me excellent over the years hate to part ways with it. Odometer shows about 225k. Motor had lifters, ush rods, ew cam, iming chain and gears, ead gasket, nd all new gaskets before i drove down from WI. I am willing to trade for a 4 door car must be automatic. Acura, onda, r toyotas preferably.