Okay, so I'm not going to do a whole deep dive here.
TL;DR - You're playing the entire spec wrong. I don't mean that as an insult, I just want to be blunt about where you're at. You fundamentally do not understand how the spec is played. I will give you a general breakdown but you need to go to wowhead and read the entire thing at this point.
1. For mitigation AND damage purposes, you want Shield Block up at ALL times.
2. Shield Slam is your #1 priority cast 99% of the time.
3. When SS is on CD you press Thunder Blast or Thunder Clap
4. When SS/TC/TB are ALL on CD, you press Revenge (Or execute if they're in execute range)
5. Use IP to prevent overcapping rage. This is off the GCD so you can hit it between abilities. Your goal is to press this any time you are at 70+ rage and are about to cast an ability that generates rage.
6. If, and ONLY if, you have 2 charges of Thunder Blast, you press Thunder Blast OVER Shield Slam. This is because Shield Slam has a chance to proc a charge of TB and you don't want to waste those by proccing when you're full charges