ht740 trans problem 96 mack mr688

got a weird issue here.
my 96 mack mr suddenly lost reverse.
this is what is happening.
no reverse, no backup camera.lights,or back up alarm. when i try forward gear truck dies.
this does not happen all the time. some times it goes into drive and engine stays running.
with the truck off, if i toggle between reverse and neutral a couple times and then start the truck, it goes into reverse,but only once it wont go into reverse again????
change the tcm, some relays, backup switch on pass side of trans. filters etc...
thinking maybe the input speed sensor is not jiving with the output speed sensor.
anybody have a similar problem? hoping its not a trans. oil looks new.
any help would be great.

 

some mechanics told me you cant get codes because its not an electronic trans? dont know how true that is though. my T shifter does have a cable to the trans not a wire.
alot of them just want to replace the tranny. but i think its a switch or some issue like that.
need help.
kind of thinking maybe nss or maybe the ign switch?