Changing tenses can work as an exclamation mark. Particularly in denoting a mental process. In other words, using past tense and switching to present tense for action scenes is something I wouldn't do - it's just too extensive, and it loses its meaning.
Examples of what I mean by "exclamation mark" (I'm just making these up, they're not from any book). Notice the mental process (flashback and inner thoughts respectively)
1) Switch from past perfect to past tense to indicate the passage into a flashback
Michael felt worried as he looked at his reflection in the mirror. Something was peculiarly familiar about those scars, he'd seen them before. Perhaps when he'd gone on that trip, the previous summer. He'd gone to the lake and had met John in the cabin. The scents were amazing, the trees emitted this amazing aroma that...
2) Switch from past to present to indicate inner thoughts
"What on earth are you mumbling about?" asked Nick.
"I told you, and I have nothing more to say", Mark said. His lips quivered, and his facial muscles twitched, as if he was suddenly nervous.
Leave me alone... I've got nothing more to say
"Come on, man", Nick insisted.