That's it in a nutshell. Water is only lukewarm (~100) even turned up to 8/10ths of max. It's a 1999 Kenmore "Power Miser 6" 40 gal on natural gas, has always been weak with the hot stuff...but it's getting worse! The flame is blueish & goes on & off normally with a thermostat adjust. I've drained ~6 gal of ok looking water from the lower tank valve. Nothings been changed in the plumbing, no leaks that we've noticed in the 1971 4/2 house. Got any suggestions?