A 3/4" home-run to the water heater more than 26 feet away doesn't cut it, not even close. Remember count about five equivalent-feet for every 90 degree ell or tee. Even if your piping lengths add up to 25-30 feet, you're probably somewhere well north of 40 equivalent feet. Figure on a 1-1/4" home-run to the water heater, and a 3/4" or 1" run for the furnace, both teeing in as close to the regulator as possible.
The K-BTU supported for the different pipe lengths and diameters are found in this matrix: