94 ford bronco with a e40d transmission won't go into 4th gear. Any idea on the problem?

The transmission has been staying in 3rd gear and it won't shift into 4th. It also tugs back and forth when it reaches 3500 rpm. It wants to shift into 4th but immediatly goes back into 3rd. Already replaced the vss and mlps. What else should i look into?

Hi if this is a manual gearbox it would need to taken out of the car and taken apart to replace worn parts.
however a automatic gearbox is a whole different issue this needs an expert to work on it as it's internal mechanisms are far more complex and need specialised tools to remove parts. And replace them. So the gearbox would need to go to a specialist automatic repair shop.