<<<I'm working on repairing a LG dryer DLE5977B that is not drying the clothes completely.>>>
Assuming the entire vent system is clean/clear...
If Fabric Softener Sheets are used in the dryer---laundry will be approximately 90% dry (on a regular basis).
This is caused by *wax* build-up on the MOISTURE SENSORS from the FS Sheet.
The waxy residue on the MOISTURE SENSORS will cause the MAIN BOARD to "think" that the laundry has become dry at/near the end of the cycle.
There are 2 options:
1) Discontinue using FS Sheets
2) Clean/scrub the MOISTURE SENSORS with a *ScotchBrite Pad* after each load in the dryer (when a FS Sheet is used)
The MOISTURE SENSORS are located on the *drum side* of the Lint Filter Housing (2 silver metal strips).
These can easily be found on the Lint Filter Housing by placing your head into the drum and looking downward at the Filter Housing.
If a *small* load has been placed in the dryer---the damp/wet laundry may not be making contact with the Moisture Sensors often enough (causing rapid termination of the cycle).
Raising the rear/back leveling legs of the dryer---about an inch higher than the front of the dryer---will cause small loads of laundry to tumble at the front of the drum (continually making contact with the Sensors).
Good job on the washer