Downloaded the Frigidaire Service Manual for Electric 5.8 cubic foot dryer from the ApplicanePartsPro.com forum. Used its information to check for error codes. None display. Ran the function test sequence. All the tests OK.
Used a mutli-meter to check the circuit to the moisture sensor bars inside the door. Thought maybe the circuit could be open due to a loose plug or broken wire. This could signal the control board that the clothes are dry. This all checked OK.
Since the top four status lights were also occasionally flashing three times in a row when the dryer was running, decided it was probably a defective control board. Ordered P/N 134484212 from AppliancePartsPro. Great service, with just standard shipping, part still arrived in two days and also well packed.
Fairly easy replacement to perform, but would get a copy of the Service Manual if possible. Great pictures in it on how to remove the top and get access to the control panel.
The replacement electronic control board comes with the plastic housing so you don't have to mess with the actual circuit board. The wire bundle was secured by a Ty-Rap which I cut and then replaced on reassembly. Two of the electrical plugs are automotive blade type. Very stiff to unfasten. I just used pliers on the plugs and worked them back and forth to loosen.
I'm slow so the replacement took about an hour. A repairman could probably do the whole job, including the paperwork, in 15 minutes.
Replacing the electronic control fixed the problem