2011 chu 613 cutting off at 1400 rpms

i have a 2011 mack chu 613 that does not go over 1400 rpms. i took it to mack dealer, they have had it for 7 working days and said they think there is a short in the chassis harness or the vecu is bad. they said they have no way to test it. WTF!! so they gave me a qoute of $3200.00 to replace chassis harness. they said lets start there does this make any sense shoundnt a mack dealer be able to isolate a problem not guess this is on top of 5 hours of diag already any help would be appreciated!!!!