Cruise control under 50-60kph ?

[Wingaman]

My truck is regularly hauling agricultural equipments(12 000 to 30 000 pound) so I looking to make the cruise control working at like 35-40-45kph.

Anyone have some clues ?

 

[Big Blue24]

Run it in third gear with a brick on the go-pedal!

I don't have any real input.....