service engine soon light, EGR code, can't get itfixed, any help?

I have a 97 mnte carlo V6,with 134,000 mi. on it. for the entire life of the car, I've gotten 31/32 mpg.(highway) ..lately the check engine soon light comes on and my machanic read EGR on the code. he cleaned it out and repalced the gasket on it , thinking it might just have a carbon build up. the vacumm check fine and every thing pertaining to the egr vavle checks ok at his shop when I leave... but a couple days later the blasted light comes back on and he checks every thing again and it still pops the egr code. we're biginning to think the catalitic converter might be the problem , but the engine has no lose of power and absolutle runs great, as smooth as silk and no lose of power or acceleration. so we haven't replaced it yet. my gas milage has dropped to 21/25 mpg.and this is really starting to bug us both. I've had it back to him at least 5 times and still the light comes on and the same EGR code registers. my budget is VERY tight and I can't afford the $200-$300. just to "try" something else. He is thinking that maybe something is not showing up untill the engine has been driven for a while and the engine is nice and hot. did just have waterpump replaced and radiator problems so had a lot of coolant slung all over the place. could that have led to anything? we're both reaching our last straw with this and I thought I'd pick you guys brains on this. any ideas?

check fuel pressure. IF the fuel pressure regulator is sticking, it will cause the car to run rich or lean. Since your mileage has suffered, I would suspect an over rich condition. This would cause an EGR circuit to trip because the car is putting more unburned fuel into the system than the EGR can reburn, so the computer thinks there is a restriction in the EGR circuit.

talked again to my machinac. he said the egr code reads as a restriced flow as the main problem. the pressures on both intake and vacumm hose on the egr valve and the valve itself checks out ok so unless it is an "intermitint" problem that is not showing up on his tests,it is fine. he thinks it might possibly be a problem in the intake itself and is going to replace it with one he has in his storage bin at no charge other that labor and gaskets. again there is absolutley no loss of power at any time,so I have a hard time believing it culd be catalic converter problems. only occasionaly some slight roughness at idle, and loss of mpg.