I have had trouble with a power loss for a couple of years now, seems as though when you get very low on fuel (light on) the car starts to drop power and bucks as the dash board power meter goes up into the max hight in the red. This only happens on long trips, just this last week on my way home from a doctor visit with the VA it was so bad that the two hour trip took four hours. Normally you can stop shut it down and restart after a few minuets and you might go for another fifty miles or just five, you never know. I have it on my mind that I have a fuel pump that is over heating and there by not giving the fuel pressure needed for proper operation. The mass has been changed as well as the ovp. how can I test the pumps for amp draw?

Is fuel pump activated with ignition?

Yes the pumps prime when you turn the key to start and when the car is running, you can hear them running too.

As a non-professional mechanic, I've learned how to utilize the services of a professional. A proper diagnosis is absolutely necessary to making the correct repair. If money is an issue, I'll simply contract with a professional to perform a diagnosis of the problem ONLY. Usually, the cost is minimal and then I have the necessary information to know what parts to purchase, factory manuals to consult, etc etc to go ahead and perform the repair service myself. Just make sure the mechanic knows Mercedes Benz automobiles and has the diagnostic software.

There might be gunk or crud in the gas tank at the bottom. And that may limit fuel flow when the tank is low.

You should be able to inspect the inside of the gas tank with a tiny USB inspection camera - one which comes with its own light.