I have a 99 f150 w/ 92,000 mile sand the 4r70w trans. The trans oil and filter has never been changed and I'm about to do that this week. My question is does anyone have suggestions on what oil to run in the trans. I was looking at getting Royal purple. The truck is used for plowing and pulling a trailor so I want to keep the trans as cool as possible. I've already installed a trans cooler and temp. guage so I know the normal trans temp.