Its a 99 2wd with 5.9 1500. It wants to take off in 3rd sometimes. I can get it to mess up if leave from a stop light and get up to about 30 then slow down to about 15 - 20 and go back up to the speed limit.. it will say in third then about 40 and it just makes the truck struggle it seems. I can pull it into 2nd and it goes and there is about a hundred rpm difference .. what could be causing this.. other then when this occurance happens it shifts perfectly fine .. it has 145k miles

 

your not exactly clear... but replace the governor pressure sensor and solenoid