After reading these responses, I must remark that this problem is similar to my trials of finding a really good way to use a thermocouple in a kitchen oven.
I have a kitchen oven that checks out O.K. with any thermometer that one would want to try: electric, NFS certified, etc. Yet, the stinking thing cooks slow, no matter what.
During all of my trials, I found that there was a normal temperature swing and that it was the average temperature for a sizable mass that made a difference. However, I have a real K-type thermocouple temperature probe for my Fluke digital meter and I tried it. The meter is too responsive and goes up and down too fast to give an average reading.
At that point, I decided to place the thermocouple in a mass, to act as a ballast, as it were. I think that the slow response of the clip or the clip attached to the grate may be an advantage towards providing accurate food temperature, since the food is a sizable mass, too. Maybe, but I gotta test this first and am out of energy right now for that project.
The oven still cooks slow, so maybe it is an air circulation problem--but turning on the oven fan does not help much.