need help with upgrading my 8 1/4 rear end.!

Well, the gear ratio should compliment the cam, converter and suite the driving needs and style of the intended purpose of the car and its driver.

Knowing what camshaft you have is a start and the intended purpose would be a great help in suggesting a gear ratio.
More driver than strip is a good description. It just leaves a little in the table for a decent suggestion.

On the rear itself, a brand new center section in a sure grip is the best start.
Following it up with stronger axles is your call. Stock axles will take 400hp all day long, all night long & into the morning.

I do believe in the past I have seen rear covers with a bolt set up that contacts the rear ends cap bolts to help stop flexing within. I think this is an extreme measure to go with and is a sign of maybe that person should have upgraded the rear end instead.

Summit racing, Jegs, Manciniracing.