2002 Ford Escape XLS 3.0L 4WD Firewall side Catalytic gets TOO HOT and melts insides?

I have melted a brand new Firewall side CAT in 2 months driving not even a few hundred (maybe not even) miles! I was told that the CAT melted because it was TOO HOT? When this converter was replaced, I had also replaced the Rear CAT at the same time because the debris from the Firewall side CAT went downstream and clogged the Rear converter. These were done in mid-October of 2012 along with a "tune-up" (6 spark plugs & a plenum gasket is considered a tune-up?... hmmmmm). Mid-November I replaced the IAC, EGR & DPFE.... but the car keeps throwing EGR codes, idles rough & bucks when you stop & have the car in gear, like the RPM's are way too low. End of December, the car was still not running right, and I had the Radiator side CAT replaced on January 8, 2013. When that one was replaced, found that the Firewall side CAT had pretty much melted to a solid piece in the CAT, so I had that replaced AGAIN with a new CAT. Got the car back ron January 14, 2013 and STILL had rough idle. Oh.... yeah... I bought brand new tires fo it that day too (not that it has anything to do with it's running right, right?). :0) So far....Since July 29, 2012 (date car purchased) 1. New Tune-up 2. ALL new (3) CAT's installed (Firewall & Radiator Side & Rear) 3. New IAC 4. New EGR 5. New DPFE January 18, 2013 drove car about 12.5 miles to my work, no engine light, still rough idling, left idling for about an hour while there, and then drove back home. Halfway back, with about 18 miles driven, stopped to spray wash mud off car (it's pretty muddy where I work), and turned the car off. Sprayed down the car, rinsed the mud off, about 10-15 minutes, and then started the car to leave, immediately threw engine light (steady, not blinking)... stopped at AutoZone and had checked, threw a P0402 (Explanation: ECM has detected too much flow on the EGR system) (Probable causes listed: EGR valve stuck open, Failed EGR pressure sensor, Failed EGR valve, Failed EGR pressure sensor where applicable, Failed EGR position sensor where applicable). Yeah, I know.... don't help much, huh? :o( Q-1: Can washing the car actually affect the EGR or it's components like this? Make it throw a code? And the EGR and EGR Pressure Sensor are new. On a "hunch" on January 19, I took the car to Meineke to have the muffler and resonator checked for debris that may have washed down past the Rear CAT into the muffler or resonator when the first Firewall CAT emptied out BEFORE it finally clogged the Rear one. Had a "hunch" the CAT installers didn't drop dropped the pipe/muffler/etc to check this. I was correct!!! Muffler had some debris and was partially blocking the flow, but not excessively. I had a new Flex pipe, muffler & tail pipe, custom fit, no resonator installed. So far now to date I have repaired/replaced..... 1. New Tune-up 2. ALL new (3) CAT's installed (Firewall & Radiator Side & Rear) 3. New IAC Valve 4. New EGR Valve 5. New DPFE (EGR Pressure Sensor Control) 6. New Muffler, Flex pipe & Tailpipe ....in the last 6 months. I am, with my limited car knowledge (at 63 I have just enough to be almost dangerous), am thinking along the line that if the muffler and/or the resonator was partially blocked enough, it did not allow the hot exhaust to escape quickly enough that it may have heated the Firewall CAT to a hotter temperature than the insides could take and that is what melted the stuff (I have no idea what you call that stuff" in there) inside it. Logically thinking, it would be about the same as stuffing a potato into the tailpipe, but allowing just enough of an opening to allow SOME of the exhaust to escape, but not ALL! Q-2 Could/would a partially clogged muffler and/or resonator do this? Here's my thinking, for you cooks out there... or water boilers. :0) If you cover a pot of water and heat it, letting it boil, and you allow just a tiny bit of room for the steam to escape, doesn't the pot boil over unless you either turn the heat down or remove the cover? Q-3 Wouldn't a partially blocked/clogged muffler or something down line of the Firewall CAT react the same? The reason I am asking is, obviously, I don't want to FRY another CAT. These freakin' things are kinda expensive, and I don't want to replace another one in a couple months again! Not for a LONG, LONG time!!! Could somebody, like a "knowledgeable" mechanical auto type person maybe, actually provide an answer to these questions? I got $2300 in repairs in this car so far, not counting the $2700 cash in it to buy it, and I STILL owe $3500 on it yet!!!! Pretty expensive for a '02 Escape if ya ask me! I just can't keep dumping money into this car like this! Any NON-MONEY solutions would be GREATLY welcomed (OBVIOUSLY... duhhhh). ;0) (the duhhhh is for me) LOL