I for one have never called Price a choker. I don't believe that he is. But I do believe he has a psychological 'monkey on his back' that's a factor.
If you read Rick Porcello's comments about his first season in Boston, he admitted that his poor start gotten into his head and 'snowballed' on him. Things do get into players' heads and affect them. Don't take my word for it, take Porcello's.