maytag dryer won't stop and won't dry

I have a Maytag dryer Model DG 7500.
Suddenly last month it started acting up after 25 years.
It doesn’t stop running on any setting and the load takes
forever to dry.
All ducts were free of lint.
Air blasts out of the flapper like always. But it’s luke warm.
I replaced the timer assembly on the console.
I replaced the valve coils.
I replaced the Multi-Temperature Gas Thermostat.
The igniter glows nicely, the gas fires up and stays on
but it is a small flame 6 inches long and maybe 1 inch in diameter.
I believe it should be 3 or 4 times that big.
Gas pressure seems fine and the gas orifice is clear of any blockage.
I can’t think of anything else to try.
HELP.

Tim Jones