I've been leasing vehicles for quite a while now. I finally decided I like the new style F-150's enough to buy one and keep it for a long time. I was thinking about replacing the stock differential and transmission fluids with some good synthetics like Amsoil or Royal Purple. I'm generally pretty hard on my vehicles, so if some good fluid will extend the life of my components Im all for it.

Transmission: 4R70W
Rear Axle: 9.75 w/ Limited Slip

The truck is ordered and should be here in about a month. Any suggestions on what brand fluids to use or when exactly to change them. I was thinking about replacing the fluids after about 1000 miles or so.

Thanks in advance.