I have two vehicles both of which have a remote lock/unlock. My car's remote will work from nearly half a mile away.

I've been amazed at how far away it will still work, and it works even through walls. It's great because when I lock it, it honks the horn. So when I come out of a store and cannot remember where the car is, I make it honk at me until I find it.

I can pop the trunk from inside the store when the guy in the feed store goes out to load my bags of feed.
Now, my other vehicle, a Suburban, also has a remote, but this thing has a working distance of about three inches.

I have to get RIGHT ON TOP of the door, and it has to be the DRIVER'S door, in order for it to work. Now, if I have to stand that close and hold the remote that close, I might as well use the key!

I've replaced the batter in the remote, but that did not make any difference.
Is there something inside the Suburban that might also need replacing?