Low Power and getting worse on INTEK 19hp (33R877)

I have a 4yr old INTEK that is slowing loosing power. (Engine Model #33R877/0008-G1)
New camshaft - 10/27/23 which fixed the broken compression relief. Seemed to run great after I put it back together.
After mowing six times this year I have low power and it is getting worse.
 
What I have done so far that has not helped at all:
Tune up 6/01/24 - Air filter, fuel filter, spark plug
Checked flywheel KEY - it was fine
Checked valve adjustment - it was fine
6/7/24 - Replaced carburetor and it runs slightly worse...won't idle all the way down
Always kept good clean oil in it. Because it lugs down more when mowing I removed the deck belt and spun all the spindles and pulleys which were fine. 
Questions:
Could the compression relief be stuck giving me low compression (hard to check and never heard of that happening)
I see some INTEK engines have head gasket problems - I see on sign of that, no oil leaks, smoke, or odd sounds.
I have mowed 1/2 acre of level lawn six times and it seems like I have about half the HP I should have.
Thanks for any ideas or things to check.
Mike
 
 
 
 

Thanks for the quick reply. The high idle DID start with the new aftermarket carb (I may put the old one back on as the new one did NOT restore power). Didn't try 'hand choke' however pushing the governor back a little does cause it to idle down. 
The cam was aftermarket also (hard to find an OEM one). I wounder if the compression release weight is not swinging out to give full compression at higher RPMS. Hate to split the block again to check it.
Any other ideas for low power? I am pretty good with small engines but I am not sure whats going on with this one.
 

It wouldn't hurt to re-set the governor as well:

https://www.youtube.com/watch?v=XbFyGRixoGA&t=411s 

I would test the engines health with a "leak down tester".
That'll show a leak internally.
 
You may be able to borrow one from an automotive  parts store.
 
 

You can just pressurize the cylinder with a "spark plug thread fitting), with the crank locked up at TDC on the compression stroke.  
 
You won't have a gauge to look at but if you hear air coming from a valve, you now know there's issues there...
 
.

Just did a leak down test and there were NO noticeable leaks! I did notice the exhaust valve gap was a little loose. Decided to roll over the engine and check both gaps. To my surprise the exhaust valve had about 1/4" travel HOWEVER the intake valve had almost NO travel. I tried to measure with a ruler and it looked like 1/16" travel at most. I guess it's time to split the case and look at that after market cam I put in late last summer. seem really odd to have trouble with a lobe??

After looking at some bad camshaft reviews on Amazon, it seems several people had worn lobes after anywhere from 20 hours to a couple years. I just ordered the OEM camshaft. I don't go cheap on replacement car parts, guess the lawn mower is no different...live and learn.
 

Tks for the update!!