It sounds like you have some mixing in the Tx. Not sure what you are working on model wise, but usually there should be no mixing. Have you tried creating a new model and starting over?
This is my problem, stick back all the way only reads 366 when it should read a full value like 966+ like it shows when full forward.. end points are all the same? what is wrong please help
Declan, are you using stock 9x firmware or has it been flashed to OpenTX?
I'll have to grab my sons 9x and do myself a quick refresher course.
I never had any problems getting it to work on a multirotor when it was my only TX.