High rev, no power on 380SE HELP!!

I own a 380SE with 234,186 miles. Over the about 1/2 a year I have owned it, I have had a horrible loss of power!! The engine is revving up high and working very hard but I can barely top 20 mph... even floored! On hills it's even worse. I replaced the fuel filter and put in new spark plugs but either one did little to help.
Someone please help me!!

[Q]

Is the transmission holding a low gear too long or slipping?

It shifts all the way up to 4th gear fine, but it works very hard trying to get it there.

[Ron Johnstone]

You didn't really answer Q's question so we can collectively help you. When you are driving with the accelerator floored and the car is doing 20 miles/hour, is the engine at a high rpm or a low rpm? Is this a transmission problem with excessive slippage or does the engine truly have no power? Has this come on gradually or all of a sudden? With the car in neutral, can you push it easily? (are the brakes dragging?) Did you change all of the fuel filters?
The more basic information we have, the better will be our help to you.

When we have it floored it will stay around 2-2.5k rpm's unless you downshift to second. I dont think it has the power to pull higher rpms. It makes a metallic clank. clank. clank. that follow engine speed, im not sure if thats harmless or if its part of the problem. I dont think there are any problems with the transmission or drag on the breaks. This problem was gradual it happened in a time period of about 1 month. We changed the fuel filter located near the diff. a few days ago but it didnt seem to help. are there any other fuel filters we are missing?
We think it may be either the lifters, the rocker arms or possibly a plugged ehaust? Thanks for your reply!

[Ron Johnstone]

With the car sitting in neutral or park, can you easily run the engine up to 4000 rpm or higher? If it runs o.k. without a load, then that eliminates many possible problems.
Was the only fuel filter you replaced a little in-line one?
Standing by the tailpipe, have someone goose the accelerator, is there a reasonable increase in exhaust or does it seem to be restricted as though you have a plugged up CAT?

[Ashman]

When my brother had the 1985 190e, we had a loss of power, you could rev it up to 4k in neutral, but if you put it in gear, the revs would stay very low, and you would not be able to get up to speed.

The cat was plugged, and needed to eb replaced.

After replacing the cat, the car was fine, until one day the tranny just up and lost 2nd,3rd,and 4th altogether.

My brother had not taken care of the car, once he had driven from sonoma, CA to Valencia CA on one tank of gas, with barely any oil in the car.

When I met up with him in valencia, we ened up having to add 5 quarts of oil.

But he did get great gas mileage on that trip... LOL

Needless to say, I would htink have the exhaust system checked like others said, have the tranny checked out to make sure its ok, and if all else fails, have the lifters checked.

My brother's 85 380SL that he has right now, just had the lifters done, and he says it has much more power than before he had the lifters done. I believe its the same engine as in your car but I am not sure if yours has the dual timing chains like my brothers car has.

Alon