Hot Water Heater

I purchased a new Hot Water Heater from Sears 2 years ago. I did not purchase the bottom of the line because family will visit, and we needed something that would recycle fairly quickly.  I purchased the unit that a salesman recommended, and had it installed a couple days later.  We got approx. 4-5 showers out of it before the temperature started to drop.  We thought that was great, and were very pleased with the heater we purchased.  Last month, we called for an in home repair because our 4-5 showers had dropped to 1-2, and we had turned the temp up.  This unit has a 7 year warranty and we paid $122 for a service tech to come out and replace two sensor units that were no charge to us.  The service tech had doubts this would help, and he was correct.  I was the second shower this morning, and had to hurry because the water was getting cold.  Our whole family is coming home for Easter, and we'll have to pick straws for who gets to take a shower.  I am very disappointed with this heater, and more disappointed with the the "Oh well, it is what it is" we got from customer service.  Also, the service tech was courteous, & very knowledgeable.  Unfortunately, the $122 we spent did nothing to fix our problem.