I am like the OP. The problem is; RPG to all of us is like making a movie in our own mind with our toon as its main character. And like the movie we expect our toons to be in character, saying the right line at the right time in the right way in front of our friends at the table, whom we treat as our audience. But reality is movies got scripts. If those actors had no script, and had to impromptu act on the spot, they would also blunder, babble, be awkward and not be so good. Yet some of us have this expectation of ourselves and others in RPG, as if that's the name of the game.
It helps not to define good role playing in dnd as an impromptu good acting on the spot trying to have a quick mind and witty response with perfect verbiage while in character to situations created by the DM. That expectation is not realistic, and can often lead to frustrations, and inadquate feeling.
It helps to define good role playing as the one you have FUN doing. You don't got to act to be role playing in RPG anyway. You already are roleplaying just by playing your paladin, barbarian, wizard...unless you are one in real life.
Relax and focus at having fun. Try not to frustrate yourself in anyway. If what you are trying to do feels too hard, trying to act out your charator for real, then don't bother. Act, talk and respond like you would if you yourself was there. After all, your charactors soul...is you.
Having a good, fun relaxing time with friends is the name of the game, and not trying to win an Oscar at your table.