To drive I must shut off overdrive and truck runs at 300 rpm at 35mph and goes up with increase speed
I've heard snap ring in the tranny or changing the solenoid block.
Does anyone know which is most likely my problem?

 

Welcome to the forum. Can you provide more info for us? Mileage? Maintenance? When was the trans fluid/filter replaced? Has it been replaced?

 

It's got 183,00 just purchased so I don't have much info prior to 45 days ago . I knew it was an issue . Previous owner told me. The snap ring for the overdrive pump needed to be replaced.
I'm also currently replacing plugs one insert at a time .