i just had the rear gears swaped out (put in 3.73's)
the shop that did the job suggested i take it easy for the 1st 500 miles then change the oil in the 8.8.
i plain on taking out the dino oil and putting in royal purple.
but
How many QT's do i need?
and
do i need friction modifier again?
Yes. always use friction modifier. If you have an 8.8 ... which you do .. and it has Traction Lock (AKA Ford's version of POSI trac) , then you NEED friction modifier. I always add it in my standard 7.5 on my 3.8. It prolongs the gear and seal life. The friction mod is usually in a tiny bottle. Pour the friction modifier in first, then add the gear oil. I always pump oil in there till it starts to dribble out the hole. Then tighten the plug and your set.
They say "Take it easy" because it takes a little time for the gears to seat in properly. If you GET ON IT during this so called break-in period, you're liable to prematurely wear them down and create a rough spot. They are usually pretty tight in place when first installed (just like engine rebuilds).