If he gets full bolt ons(H/C/I/E), 4.10's, good tune, shift kit, built trans, locker, stall converter.... Then he will be running 12's all day long.
I know one(5.3) that has all that and ran 150 shot and did 12.2..... He has the 4L60e, which is slower on the top end then the 6-speed in the newer 6.2's.
With exhaust mods and tune he should be running solid 14's with the 6.2(stock crew cab 6.2 did 15.1 last friday with 2700+ DA).
13.375
13.0
12.2