FOB only works eighteen inches from front of vehicle.
 

Changing the FOB battery has no affect.
Also, the unlock is more reliable then the lock. With the lock I have to make several attempts.
What is the resolution, how do I fix?

History:
Ten years ago I lost my original FOB and the Chevy dealer changed to this current one I am using.
Interestingly a few years later I found the original FOB.

But let’s not get side tracked.
Is the issue with the FOB or with the Car?

I've had two fobs have bad solder joints on the battery holder which caused weird problems, you might check that, also make sure the board is clean, if not clean with alcohol, denatured if you have it, otherwise isopropyl. Sadly, it could be either end.

You can order just the key pad and change that, check the circuit board for dirty contact points as mentioned clean gently with isopropyl

When one button works better than the other it’s the button. Best fix is to buy an empty case online and transfer your green board to it. Some people have had success gluing a little bit of aluminum foil to the rubber button. Clean the copper contacts on the green board with a pencil eraser,

FOB issue

1.
Approximately 8 years ago I took my car to Chevrolet Dealer to get a new FOB.
They told me they had to program the Car to the FOB and that is why they could not match the new FOB with my other FOB, and now only the new FOB will work.

2. year 2025
This new FOB now only unlocks and will not lock. I took my car to Chevrolet Dealer again.
They said they fixed this FOB. But, they did not. It still will not lock.
I asked if they could program my original two FOB’s and they said they could not.

3. year 2025
I brought in two aftermarket FOB’s. the writer kept repeating to me there is no guarantee it will work almost like that was the plan.
The only description from the mechanic was FOB’s will not work because they are after market.

4.
Locksmith said the issue is not the FOB’s. The issue is the car.

5.
Conclusion, correct me if I am wrong.
Chevrolet Dealer (1st item) change my car to match the FOB and now it is not possible for another FOB to work with my car.

6.
Is there a way to reset my car so that I can use my original FOB’s.

Yes, one had bad solder joints and the other Chevy dealer claimed to be dirty. I cleaned one and fixed the other. Dealer claimed they were still not able to program them.

I would try a different dealership

Did any one think "new batteries in fobs"? They are at least 14 years old.
It is the car that gets programmed, not the fob. If the "original" fobs are actually the ones that came from the factory there is no reason they could not be programmed, aside from stupidity. GM dealers have an aversion to after market stuff.
Your description does not indicate the car as the problem. Unless, somebody has done some unapproved programming. Once the fob is matched with the car they stay matched.

All of the fobs need to have the same FCC number. That is the key to After Market.

All fobs that you want to work need to be set in the car's computer in the same session. That is, if you set up a new fob, your old one won't work unless it's set up again with the new one in the same programming session.

DonBrew, is there a way to reset the car to original settings. Then the original FOB's should work.