Please help me with my 1996 SL600 shifting/power problem!!

[mySL]

My SL600 main problem is if I slam on the gas pedal, the car will move decently, but it will not shift out of 1st gear (red line). I steadily lose power as the RPMs go up. If I let it linger, you can hear noise and the check engine light comes on. The ODBII reading say, there is a misfire on 1 and 6 (last time I got it come up). I noticed this after I had the transmission flushed a few months. The car is also not as fast as it once was (when I bought it).

Let me give you a history which my help you guy diagnose the problem:

I have bought my 1996 SL600 2 years. I drove it back from where I bought (Rochester to DC), so I got a good feel for the power it had. It has 84K miles on it and when I brought it home, I had a local Mercedes dealer do the 90k service early. When I got it out, it did not seem as fast. I had them check it again, but they said it was fine. In fact, later it seemed to return to normal.

Fast forward to this year (about 4 months ago) and 92k miles, I had my oil change and I figured I'll get the transmission flushed since I didn't before and everyone always says if you get a used car, flush all the fluids. So I had them do it. After when I slammed on the car, the shifting problem appeared. It didn't bother me too much at the time and I was to busy to take it back to complain, so I wait until about a month ago when my check engine light came on. I found out that the manual say that an SL500 or SL600 never need to change the transmission fluid. I asked them to check the levels because they might be too high or too low. They checked it out and the levels are fine, but the Catalytic Converters have gone bad and it will cost me $3k to fix ($1200 a piece plus labor). They said they took them off and power was restored. My car friends and a couple of their mechanic friends, said that there is no way a catalytic would cause the shifting problems and they didn't believe the removed the Catalytics and drove it because it would make too much noise and they would get in trouble, so decline the service (plus it was too much) and paid $55 for the diagnosis.

One of my friends took out an ODBII reader and it said about the misfires on 1 and 6. He even asked his mechanic neighbor for opinions. His neighbor said it doesn't sound like a V12, but agree that it was not the Catalytic Converter. He recommended changing the spark plugs first and then the coils. I changed the spark plugs, but it did not help. I didn't replace the coils yet because they were $80 a piece. I also bought a transmission dip stick to check the levels. I checked it when the dashboard said 80 degrees C and the fluid was low. I check again when it was warmer (about 90) and it was fine. It the meantime, I took it to another well known Mercedes service dealer.

When I dropped the car off last week, I was wary about tell the service guy about the Catalytic Converters recommendation, but I did. He chuckled and said he didn't think that would be it. I also asked about the transmission fluid level and he said you should wait about 1/2 then check, so I thought it was probably ok. He said it would be $150 for the diagnosis. They held it for days diagnosing the problem. First, he said there was a problem with the mass air flow sensor (clips missing) and a couple of pipes that bring air in were cracked. So they replaced those problems. He also said that it would be more to inspect the car to give a full look over ($400). Today, he called me up and says what I didn't want to hear. He said Catalytic Converters were bad and it caused an oxygen sensor to fail. He said the total would be $4k to fix and that still might not fix the problem. So that is where I'm at now. He says the Catalytic Converters cost $1300 and $1350 along with the oxygen sensor; it would be the $4k. This is where I'm now.

Are the Catalytic Converters really my problem?

I can't find the OEM parts online as both dealer said they will not support parts after market. Does anybody have the part number for both Catalytic Converters and who makes it? I have found after markets for DEC and maybe CAT(?). I emailed Phil of this forum.

If I replace the coils (1 and 6), how do I know the order of them? I found this on about.com:

6 12
5 11
4 10
3 9
2 8
1 7
Front of the car

Is this right?

Also, was the service manager right about when to check the transmission fluid? The dip says 80 degrees.

Any help would be appreciated!!! Thanks in advance!