Problem Shifting Up

[Arby49]

Have a 2008 Dynasty Yorkshire with an Allison 4000 tranny. While traveling at 55mph noticed that the transmission had not shifted up to 6th gear. Couldn't run it up faster to see if it would shift up,so when I got parked, checked the codes and it gave me a P0703 code. Checked and found that I should check the wiring to the tcm. Not sure if that is something I could handle. Any thoughts?

[hypoxia]

My Allison 4000 will not shift to 6th until 57 MPH. Monaco owner manual says to put the transmission in economy mode in those circumstances so it will not keep shifting down to 5th once you get into 6th.

I do not know about the code P0703 "Brake Switch Circuit Malfunction" is what my manual shows.