The dryer heats-up but does not seem to be moving enough air. I have checked for obstructions and cleaned the duct and dryer internally.
It will dry a very small load anything near normal will take several cycles. The problem has been getting progressively worse.
Everything appears to check out electrically.

Did you check that the blower wheel was tight on the motor shaft and not slipping? Also heavy dirt/dust on the blower vanes can greatly reduce air flow.

Have you checked the lint screen, sometimes it can get coated with fabric softener residue and has to be cleaned with soap and water?

When you cleaned your vent system did you also check that the outside vent louvers opened correctly?

The following is one way to help isolate the problem.
Undo the dryer from the exhaust
Run a load
If the load dries correctly then you have a vent problem.
Clean/check the vent system. Make sure the outside louvers open fully.

If you do not want lint in the house.
Take a pair of pantyhose, put one leg into the other and attach this to the dryer exhaust.
Leave enough room behind the dryer so it can blow out like a windsock.
Run a load.

Both the above will allow you to check the air flow and temp.
Also the above is NOT recommended for a gas dryer due to possible carbon monoxide problems