I wonder if the OP could consider coming off diazepam? Consider that with tolerance to the drug (which you mention experiencing) you actually end up in mild withdrawal- which will usually manifest as exactly what you started taking the shit for anyway. Rather than cure or relieve anxiety, benzo's typically promote anxiety in the long term. I really do not think these drugs are valid tools for anxiety disorders and have been terribly burnt by them.
I get pretty bad social anxiety and have since I was about 12. I'm 35 now, this isn't going away.
But, I've learned a few ways to deal with it but they do require practise. Firstly, I would strongly suggest meditation and focused relaxation exercises. This takes a while to 'work', but what it does is give your brain a means of slowing things down so you can think of things to say and also control some of the physical symptoms associated with social anxiety like flushing or trembling voice. It gives you a little buffer to work with. Rather than simply react to what's happening, you give yourself some time to think about HOW to react.
Secondly is just forcing yourself into uncomfortable situations but in a controlled way. I'm not suggesting walking up to a stranger and striking up a conversation; start by doing really mundane things like interacting a bit more with sales-people or any people you can have a quick chat with before moving on. You will get more used to it.
The last thing I suggest is a bit of cognitive re-routing. So your voice is trembling a bit? Think about it- so what? If somebody notices, what will they think? You cannot know anyway, so this is a fruitless line of thought, but how would you react to somebody with a trembling voice? Would you run screaming that there is an alien amongst us, or would you more probably just briefly think 'their voice is trembling' and move on- or would you even notice? For me, I reaslised that I wasn't working around judging peoples weirdness because I was so focused on my own, and most people are like this. Despite how it feels, if you have a conversation with most people, they are thinking more about how they appear to you then they are thinking about you.
Try to notice your safety behaviours. These are usually adaptations we make to try and cope with our anxiety, and they often take the form of avoidance. They may make us feel safer and less anxious in the short term, but because they do not really address the actual problem, you will find yourself creating more and more of these safety behaviours and your anxiety will worsen. If you talk to a person, and your voice trembles, you are not going to die. Nothing
truly bad is going to happen; the worst possible outcome would be the person thinking you are a bit weird. On the other hand, when you try and avoid this minor issue you end up having to avoid heaps of your actual life, and this IS a bad outcome.
Trust yourself. Humans are social animals, we evolved to talk and share our lives. Trust in your ability to innately do this. If you spend most of your interactions worried about how you appear to others, of course you won't have time to consider engaging in conversation. Try and redirect your thoughts towards a focus with more utility. And rememember, you don't HAVE to be like other people. Just be yourself and nothing much else matters.
My own social anxiety is still present but it impedes me much less than it used to.