My 3126B, 3000 series will upshift at 2650 RPM, during exhaust brake operation.
When I need to apply the service brake at 2500 , I only drop the RPM to 2000.
Below 2000 the trans / exhaust brake program will downshift to a lower gear; to keep the engine RPM in the optimal exhaust brake performance range.
The exhaust brake performance graph , is the last in the attached pdf. The chart goes to 2900 rpm and that's the manual transmission equipped engine's max operational RPM when using the exhaust brake.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.