New O/O with Freightliner FSS shifter questions

[baileydale]

Been thinking about buying my own for some time now and got offered a deal that made up my mind, I already know I'm crazy so just welcome to the fold !!! Now for the question, I bought a 99 Century midroof with a Freightliner FSS 10 speed, when I tried out the truck the owner didn't go with me and I had no idea how to run this trans, I finally found a switch on the shifted that slides up/down..slid it to off and , I thought I shifted it like a normal Fuller 10. Today when I took possision of the truck the previous owner tried to explan to me that when you turn this feature off that you just went through the gears without any manual change between lo/hi range. That the truck knew when you were going from 5th to 6th by speed. That just doesn't seem right, we didn't have time to run the truck again and I may not be able to run it with him at all, I know I can figure it out but any help would be nice The shifter has a toggle switch on the left side ujust right for the thumb and a slide switch below that that shows the word off when slid up and on when slid down. Thanks in advance, I have learned so much here and maybe can sometime help someone myself.
David

[big truck driver]

sounds like a 13 speed

[baileydale]

I wish.....just a 10 like I haven't seen. Regular 10 shift pattern on the dash but the written instructions leave a little to be desired for these old eyes !!

[century451]

The off and on is that...an off and on switch. Off it shifts like a 10 speed and the rocker works the hi and low side of the transmission. With it on the rocker is used to shift up or down and the computer matches everything to shift without a clutch.