Please provide the following when creating the Ticket:

Version: 1.4.0.22
Modded?: (No)

Issue Description:
This issue references ticket T177770 which was closed as a non-bug feature

While operating HMMWV's, and any M923 5ton trucks in drive. They will use engine braking to aggressively reduce vehicle speed to approx 5mph.
No HMMWV variant has ever been equipped with an engine brake (Jake Brakes). Or even exhaust breaks that do the same thing.

The same goes for other contemporary vehicles that used disk, or drum brakes like the M1008/M1009 CUCV's, and the civilian K5 Blazer's that they were based off of.

Likewise the M939 family of five ton trucks (to include M923's) did not have engine brakes built in. Which would be evident in the -10 level TM's.

Jake Brakes do however show up in the TM for M977 HEMTT 10ton trucks. Which were introduced in 1982, and were contemporaries to these vehicles.

I would also like to point out that engine brakes historically have been loud enough that many towns forbid their use, and will fine truckers for using them inside city limits. Which is why you see them attached to physical switches inside the cab of trucks.

Also. Assuming HEMTT's get modeled in future releases of this game, and incorporate Jake Brakes. The amount of break force felt was significantly more than my albeit limited experience driving HEMTT's.
At max setting, and with no load. It's less efficient than using breaks at 20-60mph (32-97kph), and around 10-20mph it's basically not affecting you. Which may not come across with a keyboard as well as an analog gas pedal.