Hi, Welcome to the forum.
To me it sounds like your not letting the oven heat soak long enough. I usually get the top to about 1000 and the floor to about 800. It takes me over an hour to do this. To heat up the floor you need direct contact with a lot of hot, glowing coals so I start with a good sized fire to generate the coals and keep adding wood (3-4 pieces at a time) to keep the blaze going.
I also start the fire right where I’ll be cooking and, as I add wood, I’ll grow the fire towards the back of the oven so that I have primarily coals in the front and most of the fire in the back half of the oven.
Typically I can cook 5-6 pizzas before the deck gets below 600 at which point you move the fire around to reheat. Some people move the fire side-to-side. I’ve tried that but have settled on pushing the fire to the back while cooking.
One other hint: Don’t give up It took me quiet a few attempts before I found a method that gives me the results I want.