Thanks to the group for all the great information. Wow, do I have trouble!

I do not understand how the age or type of oven would have anything to do
with the question of acceptable temperature ranges.
Does the food care if the oven is gas or electric or hardwood under brick?
What I thought should matter is the allowable temperature fluctuations.
Then the trick is to get the oven to operate within those limits.

Since I may be all wrong about this, here is the info some requested along
with a warning about really horrible service:

This particular oven is a Maytag Gas, with an additional electric top
element for HIGH broiling only, (not used for baking or convection
operations) It is Very High End for home use but not too many bells and
whistles (e.g. no grill, or griddle, or charbroiler) just an oven and four
burner gas range top. It is high end for home, but nowhere near the
industrial or restaurant grade! It is now about three years old. The unit
is supposed to be state-of-the-art solid-state technology (therefore,
quicker and more accurate temperature control at all settings (LOL), but
somebody forgot to tell the oven!) I bought the thing at Sears and went out
of my way to get the best, even though it was well above budget. This
problem has existed literally since day one. So far, we have had two ruined
Thanksgiving Turkeys, (literally used my BBQ and Coleman camp stove to
finish the meals, a few hours late!), countless ruined meals, and have
thrown out 85% of everything attempted in the oven, the other 15% barely
passing as edible.

Sears has been less than worthless in its repair or maintenance coverage.
The worst thing I ever did was buy their Maintenance Agreement (so far this
last round of non-repair from their customer NO-service department is taking
more than six weeks, with no end in sight.) FYI my clothes washer has been
out even longer than that and both are still inoperative.

Each time they come out, they pretend too tickle the appliances. They use a
shotgun approach, (never even take out a multi-meter!) and order ONE (and
only one) of the many "possible it could be any one of these bad parts"! I
notice they usually order the least likely but the easiest to replace part.
Then they re-schedule service for a week-and-a-half or two weeks later, at
which time, (surprise!) the part still has not arrived so they
re-re-schedule another two weeks out (even if the part arrives the next day)
and since that part was not the problem in the first place, they pick the
next easiest part to replace and start the whole cycle all over again, and
again, and again, and again. . . . Meanwhile, no washer, no oven, no
holiday goodies, no sense of hope! Lots of worthless platitudes and
apologies, but no service, no help, and certainly no real effort to be of
any assistance. Calls to Chicago head office result in more "Take it or
leave it" mentality. It is worth observing, they were not as apathetic about
collecting their MA fees, up front!

Anyway, thank you all for all your wonderful advice, references, and solid
opinions. I can see this is a great group and I hope I can return the favor
in the future.

Sincerely,
Bob Giel,
Los Angeles, California