First of all...what brand of water heater did you buy? It makes a difference. Cheap water heaters on eBay may not be the answer. Was the water heater the correct size for your needs? Did a reputable company size it and install it? Do you have circulator loops on the the offending plumbing branches? Did you buy it thinking you were getting "instant hot water" which they do not provide? (They provide continuous hot water...not instant. You must still run the cold water out of  a line before you get to the hot water.) And where we come from, common, or standard, gas lines are NOT only 3/4". Gas lines are 1" (minimum) if the first appliance branches off in the first 40 feet. If it does not, then the line must start out at 1-1/4".

If you bought a discount house brand, didn't get it sized correctly, expect it do do more than designed for...you might very well be unhappy. And by the way, one thing you didn't mention is that these water heaters do require annual maintenance...the frequency of maintenance depends on the quality of the water. Get it serviced along with your furnace or AC unit.