I would absolutely stay with what you have.
You gain neither lower miles, better fuel economy, knowledge of the history of the vehicle and give up any sort of 'truck' capability but the Toyota glazers will love you for it.
My F150 with the 3.5 Eco just turned 186k over the weekend....I have only put new exhaust manifolds and two coil packs in that time and like you, it rides and drives as smoothly as new.
My Tacoma at that stage was rotting from the inside and needed significant mods just to make it down a fire road.