HDM,

What do you mean by "dwindles over time" ?

Are you using Natural or L P gas ?

You should have one size flame, from the time the burner ignites until the thermostat opens and the gas valve solenoid closes.

Based on your dwindling flame, you may have a gas flow/pressure problem or a problem in the internal components of the gas valve.

Good Luck,
:) :) :)

HDM,

Thanks, that's what I thought you meant.

First check and make sure the glow bar igniter is remaining orange and is partially, in the burner flame.

Then,

Like I posted previously, The flame size should remain the same size, color, etc. from ignition to burner shut down, when the thermostat opens and removes power to the gas valve coils.
You should have the Gas supply company or a servicer, come out and check the gas pressure on the dryer, "under a load". the pressure should start and remain at 3.5 to 4.0 WCI, while the burner is open and you have a flame, after a few burner cycles.
Otherwise you'd have a bad gas valve,

Part number: AP4047140