I build allot of Saginaws for circle track and we race them in our sportsman car. 530 HP turning 7800 rpm. No problems to speak. Here"s the secret GL4 oil, not ATF. I use Amsoil Manual Transmission & Transaxle Gear Lube 75W-90. never had any issues yet. Make sure you start off with a rebuild kit in it. These trans are all over 30 years old now. Buy a kit or bring it to a reputable builder. The Saginaw three speed has the lightest rotating assembly out there, thats why they are quick!!!!