tier 1 trucks were pretty simple i dont remember being able to limit speed thru the ecu (at least on the mistus)
on tier 2 mitsus the tranny is intergrated into the software thru the vcm (vehicle control module)
i do believe (but not 100% sure) that u can limit the speed thru the VCM

most electric trucks you can limit the top speed too thru the software
including ge controls (limit the % of power to the motor on the throttle and disable the a1 function or rabbit speed)

supplemental speed limiters are pretty much for older machines at this point in my opinion

as far as seat belt switches and operator presense switches
operators will figure out how to bypass the seat switch in a day and the belt goes behind the seat and stays pluged in all the time
even on the linde er18 where the computer recognizes that you didnt unplug the seat belt and wont go until u release the belt and put it back in operators just reach down pull it out and put it back in with the belt behind their back or the seat back

i tell them it would just be easier to wear it then to go thru all that
if that encouragment fails i describe in vivid detail how a forklift tips over and tends to snap down like a mousetrap
and that it is most likely that they will be decapitated, disemboweled, or their skull will be crushed open like a watermelon thrown from a 5 story building

the latter tends to have more effectiveness
but most people are dumb and stubborn (including managment) and this almost too often proves to be a deadly combo