At the risk of dragging up the dyno is only a tuning tool etc argument...250kw (335hp) for those mods and that cam seems a little on the low side. Imo you should be looking around 280-300kw.
This guy is closing in to 300kw, same cam on an ls1 (video loses audio during the pull unfortunately)
I have the following in my vx that I had tuned just before xmas at 267kw (358hp) on a stock cam.
1-7/8 4-1 Pacemaker headers
2.5" catback
100 cell cats
VCM OTR
3.9 truetrac diff gears.
Stock cam (as far as I know)
Dont know about your converter but maybe have another chat with your tuner !!