How to determine the needed stall speed?

X2
My converter was a custom build, BUT it was a cheap $150.00 one.(stock 11"converter tweaked) Was built to stall at 3000 NOT! Pulled it back out and and told him it stalling at 2200. he re did it and now it stalls at 2800.He said i would have to go to a 10" to get any more out of it.
I'm sure there is a lot left on the table because of it!
and is why i can't brake a 2.2 60' time, even with 4:56 gears. ](*,)