with your car running stopped. Is it notchy going into 1st and rev? Thats the 1st sing of your clutch isnt relising all the way witch it sounds like. As the catch point rose afetr the 1st 20-50 miles is it still relising before top of the master travel?
Don’t use royal purple in a T56. Mobile1 ATF I like using.
Did you bench bleed the master? What shifter do you have. Sorry for all the questing, the LSx hydrilics are super pissy about all this.
There a fill level plug in the side of the case, your see it. you can fill it tho the shifter too. car level a dry trans Fbody T56 take just under 4qts.