T.W.
First of all it's a process that takes time and some longer than others. If he was a she then it would be easier on YOU. She could go when you go and see how it's done.
I have 2 boys and a girl and I'll tell you what we did. All 3 were different. So, I'll just tell you what we did for the youngest which is 4 now.
1.Take the pullups away and only use them at night to go to bed to start.
2.When he gets up in the morning take him straight to the bathroom and have him go pee. Then put underwear on him.
3.When he's eating breakfast or shortly after finishing ask him if he needs to go and keep asking him every 5 or so minutes. I know it's daunting, but a little hard work in the beginning will go a long way.
4.Reward him with praise and kisses when he goes to the bathroom. And tell him he's being a big boy by using the big boy potty.
5.Tell him you are going to a pee pee party and everyone has to go. I know this sounds corny but if you make it funny or a game you'll get a better response.
6.Have your husband take him when he goes, so that he can see how he's supposed to do it. Plus, going pee pee with daddy for a little boy is big fun.
7.Eliminate any fluids by 7. My son goes to bed at 10 or sooner and we stopped letting him have anything to drink after 7 (PERIOD), don't worry you are not being cruel he'll be fine until morning and you'll have a dry bed.
Once he goes a month without peeing in his pants or pullup at night you can completely take all the pullups away.
Now, you will be doing a lot of laundry to wash all of those pee'd in pants, but buy a pack or two more and hang in there.
As far as the bowel movements go it's very odd for them and a very odd sensation for them so they want to hide when they have to do it. It's a natural thing. Just make sure that you keep asking him if he needs to go after eating.
He'll have accidents for a bit, but don't worry he'll get there. My youngest wanted me to stay with him while he went to the bathroom everytime, he was afraid to be alone and if the ac came on while he was on the toilet he would freak (the vent is over the toilet), he thought a toilet monster was going to eat his butt. It was really pretty funny at first, but became very annoying.
Needless to say, he goes on his own and lets you know when he's done.
Good luck you and he will get there.