converter slipping

ok....apart from my turbo oil leak it feels like my converter is slipping. when I took her for the first rad test I thought the trans needed more fluid, but no that was all good. the shifts are softer than I would have expected also.
my converter is a 9.5 ptc 3800 stall. 410 sb, s475 turbo, 727.
the rear gears are 3.5 and a 28" tire.
at 60 it mostly sits around 2200rpm but sometimes gets uo around 3000 but mph does not change much. when I give some gas it reacts like a manual with a f#@ked clutch. give her a big foot full and around 3500- 4000 it explodes into life, boost coming on strong too.
i'm running a large cooler and it does not seem to be getting hot at all.
I read somewhere that sliping and softer shifts go hand in hand. higher rpm the shifts are firm.
what gears and tire are you guys using for a street stripper. maybe I need a higher numerical gear like 3.25 or 3.5?

cheers