Diesel in low range steep grade E brake question

[JayLeonard]

Today we took the truck up and down Mt Washington (NH). Going down in first gear tow/haul with the E brake on wasn’t keeping the truck slow enough without leaning on the brakes. So I put it in 4 wheel low and 3 rd gear was just about the right speed without hitting the brakes. But a few times the speed creeped up and rpm’s got just a little over 2000 and the truck started bucking like crazy. Hit the brakes to slow it down and bucking stoped.
Was this caused by the injection pump defueling?
Or what? Anyone experience this ?

 

[DA67Goatman]

Needs clarification: Engine brake or emergency brake?

 

[2020PW]

It’s normal, sounds like you right on the low end of the operating condition threshold.

 

[crash68]

Needs clarification: Engine brake or emergency brake?

neither, it would be Exhaust Brake, standard on a Cummins.

Going down in first gear tow/haul with the E brake on wasn’t keeping the truck slow enough without leaning on the brakes.

Which mode? Full or Auto?

 

[JayLeonard]

Engine brake on full mode.