I know you replaced your water pump recently, but it really sounds like the water pump. I recently changed mine and the replacement had a damaged plastic impeller that failed shortly after installation. I finally ruled everything else out and took the water pump off and voila... plastic pieces everywhere. I was fortunate to be able to fish all the impeller parts out of the engine block.
I put new water pump on and ran water through for a final flush and had heat in the cab finally so will test drive and see if it overheats. Thanks everyone.