Transmission stuck in 3rd gear problem

I can help you thru all the steps lets start by checking the pressure. First remove the air box in front battery bellow that you will see the transmission filter. Right next to the filter is the transmission temp sensor its little. Unscrew the temp sensor and remove it then screw in the transmission pressure gauge tester adapter. Then start the engine and make sure there are no leaks. It should read about 60psi. Then pull the line pressure actuator fuse it should read a min of 175psi but most of the time will read well over 200psi. If it reads bellow 175psi give it a little throttle see if the pressure raises over 200psi. Let me know what you find.