Yes, that close to the stove outlet it's going to be high compared to what others get taking their pipe readings farther away from the stove.
Even with the ash door dampers only open a sliver your getting more air added through the leak. And you may be able to run the stove on less than the 3/4 open of the stack damper.
Since you have air coming in through a leaky ash door, here's an experiment you can try until you get that ash door to seal better. Let the leaky door be your ash damper opening. See what temps the stove puts out with both ash door dampers fully closed.
If you have the type of stack damper plate that has some holes in it, try closing it all the way. See what that produces in the way of temps. Don't close it all the way if it's one of the solid type pipe dampers without holes.
Another question. What size coal are you burning ? Some stoves run slower on smaller size, such as nut.
I can't get stove coal here only nut. But, I've found that by picking out the biggest pieces of nut and testing using just those in the stove, my range runs very hot and tougher to slow down. If I were just using it to cook, the stove would work faster/hotter and that's what Glenwood says to use in this.
To live with the air leaks this unrestored range has (until I can get together all the parts I need to restore it), at night I pick out the largest pieces of nut coal and put them in a box behind the stove to burn during the day. That gives the firebox more coal density (more fuel per cubic inch of firebox), and smaller air spaces between the coal chunks (slows the burn rate). The results are that it is more controllable and runs slower and longer through the night. The large chunks that get picked out make for quicker heat up and higher temps for cooking during the day. Once it's properly rebuilt coal size shouldn't mater as much as it does now.
It'll take some experimenting with coal size to see what your stove and draft prefer, but it will show you what works best for your set-up. And, you get to stay nice and warm while your testing the stove !