I think your hammer drill is hammered out. I killed a Milwaukee cordless with too large a bit, going through my foundation. Made the noise but didn't hammer any more after a few holes.
You must have very hard stone too, also why do you need a 3/8" hole? Flat screens are pretty light these days so you could probably go down in hardware diameter.
For bits, I've had good luck with the good brands at home depot, Milwaukee, dewalt, etc. Get as set of those and they should last a long time.
My second Milwaukee cordless finish the job with a smaller diameter masonary bit and lived a long time after, so maybe get a milwaukee or rigid heavy duty cordless as well with a 1/4" bit.