It sounds like you're just throwing parts at it rather than diagnosing the problem, which isn't really an efficient way to repair a vehicle. Test your fuel pressure and see if it's at factory spec (Fasteddy just wrote a post on how to build a fuel pressure tester). Your converter can be tested by measuring the temps at the inlet and outlet - a properly functioning converter will have hotter outlet temps than the inlet. If you can weld, you could also weld small tubes into the the exhaust pipe before and after the converter and use a pressure gauge to compare the pressures - a significantly higher pressure before the cat meas it's probably clogged.

Whatever you do, don't replace any more parts without diagnosing beforehand - they're costing you time and money and you're not fixing the problem.