How to use Real Automatic gearbox

[Arkydave]

I've always used simple automatic, but want to move to real automatic and, eventually, sequential. I have no wheel or pedals, only keyboard, mouse and XBox controller. In options, I have changed gearbox setting from simple automatic to real automatic, and keyboard settings have down-shift set to control key and up-shift set to shift key. I'm driving an default Kenworth truck. When I start up, the gearbox shows "A4". Pressing the control key twice, the gearbox goes to "N" and then to "R1", but when I try to accelerate, it changes to "N". I feel that there is something else i need to change in options, but don't know what. Any help? Thanks.