TB, you're right about Sonny for the most part. But Sonny's mean words said to Tom were the product of Sonny's temper, nor disaffection.

On the other hand, I've maintained for years in these threads that Michael blamed Tom for the Corleone's misfortunes (so have some Board members). Following Michael's introduction of Tom to Kay as his brother, Michael states that although Tom might become Consigliere, he's not a Sicilian. After the hospital thing, it's Tom who advocates waiting and it's Michael who opines "We can't wait." which cements Michael's negative opinion of Tom.