As posted elsewhere on the forum:
The gas engine (B58) gets the 8HP51 version of the ZF 8-speed, which has a max torque rating of 500 Nm or 369 lb. ft. of torque.
The diesel engine (B57) gets the 8HP76 version of the ZF 8-speed, which has a max torque rating of 750 Nm, or 553 lb. ft. of torque.
From the UK brochure:
The lower torque rating of the 8HP51 becomes a concern for
some people, who have expressed concern about the power of the B58 in the Grenadier, which is 282 HP and 332 lb. ft of torque; the Grenadier is heavy (5,875 pounds for the gas version), and
some people feel that it might be under-powered. Note that concerns around this topic vary considerably based on the elevation a person lives at, the intended use for the vehicle, and a person's expectations. A common solution with a forced induction engine is to tune it for more power (it is typically very easy to tune forced induction engines). However, the max torque rating of the 8HP51 is just 11% higher than the existing torque output of the B58, so there isn't much headroom there.
Many people are not concerned about the power of the B58 in the Grenadier, and so are not concerned about the difference between the two transmissions. That's a synopsis of multiple discussions on this forum on this topic.
See table below for a summary of the ZF 8-speed transmissions and their applications:
