i got a 91 bronco and the transmission has been acting up lately. it has always shifted hard since i got the truck. i changed the fluid and put some lucas transmission fix in it. sometimes when i drive it on the highway it changes gears for no reason. it down shifts like its trying to acclerate even though i dont press the throttle when it does this. someone said it might be the modulator on the transmission. i think it is a c series transmission......anyone got any ideas?