Thanks for the replies Randy and Larry,
I got the dip tube out and it looks fine.
So now I’m baffled. The problem acts just like a bad dip tube.
No changes in plumbing have occured so it’s not a cross connection. The only cold line is the one feeding the tank. We have no recircs in the house. Though I’ve thought they may be worth it.
I’ll have hot water for a short while then it starts getting cooler to just warm.
I did screw up removing the dip tube. I thought it was right on top under the water inlet line, but as it turned out what I was trying to remove was a plastic check valve in the metal nipple if I have the correct term. So I removed the metal nipple (short double male pipe) and underneath it was the dip tube.
? Cold cool water actually leaving the heater? Not sure what you mean.