Something definitely sounds out of wack if your
fuel consumption is that high. The natural tendency is to immediately blame the engine although there is often a different culprit. The energy has to go somewhere so you are either not burning the
fuel, it is being lost as heat, or it is being lost to doing useless work in the water.
The first thing to look at is the person operating the throttle. Do you like to motor around at hull speed and 3000rpm? The fastest way to increase
fuel consumption is to throttle up. If you motor around at 2/3 of hull speed, then this isn't the issue.
What are you running for a prop? Is it a very inefficient blade design? Is it damaged or fouled with sea life? Is it properly pitched? You can tell that this is in the ballpark by making sure that you can reach both hull speed and redline rpm.
It is unlikely that the problem is in your shaft since there would be another problem to dissipate that much energy. It is possible that you have a transmission problem. Does the transmission operate normally? Is it scalding hot to the touch?
Then you get to the engine itself. The first thing to do is check all your filters to make sure that they are clean so that the engine is getting good
fuel and air. Then take a look at your
exhaust, is there a lot of black smoke under load or unburned fuel coming out? If something is coming out, you have a problem which needs to be diagnosed. A poorly tuned engine will get worse fuel economy but it is hard for one thing to make the engine burn double the fuel. Valves that are out of adjustment will decrease fuel economy but by something like 10% max. If the engine's timing has slipped, that can have a very large effect.
To answer your original question, I doubt that you will see large improvements from getting your injectors rebuilt unless there was a major problem beforehand. Your injector tips can get carbon buildup on them which causes the fuel not to atomize as well but this usually does not have a large effect. In addition, over time the holes in the injectors will get larger flowing more fuel less efficiently but this doesn't have a huge effect. If one injector was hanging open, you could see this drop in fuel economy but you should have noticed other problems as well such as black smoke, unburned fuel in the
exhaust, the engine not sounding right.
Unfortunately, there are a lot of factors at play. If the problem is in your engine, a good ear should be able to hear the problem the vast majority of the time. Don't rule out all of the other factors too soon.
Good luck.
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Rebuild Injectors - Fuel Consumption?
Most other T37C owners say they average about .75 gallons/hr so I know something is out of wack. (I have a Westerbeke 50 41hp 1980's era with about 3500 hrs) 
LOL
