Re: 5.7 with 280 vp gear oil?
I pump mine up through the drain hole as well. Just keep an eye on the dipstick. I've never removed the fill plug.
#1. I have filled a great number of these drives. Easiest way to get it right is to pump it up from the bottom thru the drain hole until it comes out the fill hole. Reinstall the fill plug and the dipstick and you won't loose much fluid when you disconnect the pump. Works every time the first time.
#2 Please tell me you have put a drive shaft bellows on it. If not, save LOTS of money for a drive rebuild, new bell housing shaft and bearings, new u-joint assembly and possibly a new bellhousing. Removing the engine, drive and bell housing.
I pump mine up through the drain hole as well. Just keep an eye on the dipstick. I've never removed the fill plug.