Is my adviser stalling or am I being plainly lazy?
Since everyone here seems to scratch their heads about what might be going on, my first reaction is that there is a breakdown of communication between you and your adviser. It clearly doesn't make sense to do 100-page long computations on paper if they can be done by a computer. So the reaction of your adviser doesn't seem to make any sense -- but what stands out to me is that you don't seem to talk to your adviser about the situation.

Talk to him about the issue. Have a conversation, understand his motives, discuss why he wants you to do these calculations by hand and why he doesn't seem to trust the software. He may have good reasons, but you'll never find out if you don't talk about it. At this point, it's all speculation when you could have a conversation to actually understand.