gr33ngo,
Could you give us a little more information. Has the car been sitting for a long time before you got it? When it won't accelerate, does the RPM go up but the car doesn't move? When this happens is the engine still smooth or is it running rough?
I have an 84 500SEL and I assure you it will go up any driveway I have ever seen. These cars were built to run 140-150 MPH all day long, and that takes Power.
If you could help us get a better idea of what the car is doing I am sure we can help. Please don't just throw parts at it until it runs correctly. If you do it may end up being the most expensive car you have ever owned. On the other hand, if you only replace/fix what is needed it can be the best and least expensive car you have ever owned. We can help.

PaulM

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84 500 SEL (307,xxx miles)