18 SPEED SMART SHIFT PROBLEMS

I have a freightliner with a C15 pushing an 18 speed smart shift. It shifts perfectly from 1-4 then shifts into 5 but no throttle response and the 5 remains flashing. the motor keeps giving small revs as if to match engine speed to road speed but it is already in gear so the trucks jerks every time it revs. this goes on for about 5secs and then you get throttle and can continue driving however the number 5 will still be flashing and the jakes will not come on at this point. 6,7 and 8 do the same 9 through 12 is perfect but 13,14,15 and 16 the same 17 an perfect. but usually in the morning when you start off all the gears work perfectly and then after a hundred miles or so it will start this problem when everything is hot. Any ideas on how to fix this please?

 

Yes, l have no fault codes on the vehicle.

 

Well i'll let you know if l find the problem.

 

Well l opened the box today and all looks very good. So im thinking about swoping out the XY shifter.

Any other suggestions ?