96 Hyundai Accent gt

Po135 computer code o2 senser heater circuit malfunction bank 1 sensor 1 has been an ongoing problem. The car has 134,000 miles and runs great. I have tried a new sensor. A new factory sensor. A used computer. A second used computer. My repair shop hooked up his snap-on scanner and checked everything. The o2 sensor is working and the heater circuit appears to be working. He has driven it and graphed the sensor. He has checked voltages. He has ohmed the wires. He has added supplementary grounds. When I take it through the drive cycle, the light comes on again with the same code. The o2 sensor test and the catalyst test do not complete. The heater circuit does complete, but sets a code. Any ideas? The Hyundai dealer said after $250 worth of diagnosis that it could be the fuel pump and the fuel pump regulator. They said I need to replace them both. It runs fine straight up a hill at full throttlle. I did replace the regulator. My mechanic says it is bunk, a heater circuit malfunction has to be electrical. I like this car. Should I try another computer, another O2 Sensor or another mechanic. Please help. Jay