Is it possible to run HDLC bus at 2000kbps on a Rabbit 4000 ?

Hallo, we are trying to Tx & Rx data to a sensor using HDLC on a Rabit4000 module. When using a synchronous bit rate of 500 kbps the transmit and receive works fine based on example code supplied. However, when trying the same at a higher rate: 2000 kbps (2Mbits/s), we experience an Abort sequence during transmission and no reception.

Therefore:

Are there any known upper limits for the synchronous bit rate of a rabbit4000?

Has anyone in the community used the rabbit4000 and its HDLC software with data rates of 2Mbit/s or higher with success ?

Thanks for any help.
kind regards
John