While the previous gen had a problematic HG design, there were also many other contributing design factors under the hood that stressed the HG design.
All of those contributing factors were corrected with the next gen 6-spd LBZ (LLZ).
However, as time has progressed, we've also found out that GM continued using the old style HGs on the early '06 models, until inventory was depleted.
Later '06 models had the newer updated HG design. Being an LLZ, it also has the old style HGs. However, that doesn't mean the HGs are destined for failure.
Because all of the contributing design flaws were corrected.
Checking balance rates on a hot engine, 'can' show out of spec rates, but it's not the end-all of diagnosing worn injectors. A return rate test is more definitive.
But as I've found out, there's not many shops that have the ability or knowledge to properly measure return rates.
Rail pressure;.....with a hot engine, hot fuel, rail pressure 'desired' levels not keeping up with 'actual' levels, can be caused by excessive return rates from worn injectors.
But the rail pressure not keeping up, can also be 1 or more of 6 different things as a cause.