Why does rpm rev to 3 rpm foot off gas pedal and no pull

Hello, you didn't indicate which engine your F150 has. But, no matter. Either way, diagnostic testing is needed - performed by a skilled and trained and experienced technician with proper diagnostic equipment and workshop manuals for reference. There's no way at all to figure out what's going on. Not sure why you'd mess with a transmission if you don't have proper tools to replace needed fluid - this is something best left to a professional. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops