A couple of evasive issues

[e39 5ive]

Well here it goes. Just got my car back from a second mechanic, as I refused to believe the first mechanic when he told me nothing was wrong with my car. The second mechanic can't find the source of my problems either. Here are the issues I'm having:
1. This is the one that really annoys me. Car has a vibration/grumble sound @ 40mph. Seems to decelerate quikly, almost feels restricted too. No vibration in the steering wheel, but around my foot area. No one has been able to tell me why. Flex disc, u joints, and driveshaft all seem to be totally fine. Originally thought it was my struts, as they were in need of replacement. However after installation of a set of Bilstien all around, the noise and vibration remained. I run a set of staggered wheels 18x8.5 front, 18x10 rear, but even with the stock wheels and good tires the problem stays.
2. My mpg gauge is on some type of delay. I press the gas and the needle takes a second and then pins itself at 8mpg as if I'm gunning it. As the car changes gears the delay remains ultimately settling at the 25 - 28mpg range at normal highway speeds 70 or so.
This time around, I might add, the second mechanic told me I have an oil cooler leak. So that's something I'll be adressing soon.
I've been checking in on a couple of previous posts, and have also checked through archives, all seem to be dead ends. Or at least I've found no answers. Hopefully someone can help me out.
Much appreciated,
E39 5ive

[saltshaker185]

auto or manual? and whens the last time youve changed your tranny fluid and rear diff fluid?

[e39 5ive]

Auto, and I've done neither services. 108,000 miles.

[LOS]

Do you experience the same vibration when the car is running in "park" and step on the gas? Or is it only when it's moving?
Have seen any leaks coming from your differential? Does it look wet/oily in that area?
You said you looked at the drive shaft, did they tighten the bolts to proper torque? These bolts are known to come loose!
to answer your questions above...
My 540i decelerates quickly as well. This is normal on V8's with an auto transmission. The vibration part, not normal
The needle comment you had is also normal, is not a problem.

LOS

[ozarkmark]

Originally Posted by e39 5ive

Well here it goes. Just got my car back from a second mechanic, as I refused to believe the first mechanic when he told me nothing was wrong with my car. The second mechanic can't find the source of my problems either. Here are the issues I'm having:
1. This is the one that really annoys me. Car has a vibration/grumble sound @ 40mph. Seems to decelerate quikly, almost feels restricted too. No vibration in the steering wheel, but around my foot area. No one has been able to tell me why. Flex disc, u joints, and driveshaft all seem to be totally...

That is exactly what I am experiencing so I replaced the front left bearing to no avail. It would get louder if I turned to the right therefore I thought a bad bearing was the issue.
I will probably take it to my mechanic soon and will keep you posted.