If he rebuilds the 4L60E, that in and of itself will not help him LAUNCH more quickly.
If he upgrades the torque converter, does not do enough research, and buys the wrong one, he'll lose low load / light throttle drivability, lose metro / urban MpG, and will still be held back by 3.42.
Plus a torque converter upgrade also requires an ATF cooler upgrade if you want the transmission to last.
All that'll cost more than a 4.10 WITH a torque-sensing limited slip diff, and the XL with 4.10 will still beat it in a race too.
All while getting better metro / urban MpG and keeping the 4L60E cooler.
(Nothing personal, mountie ...)