Help with sluggish 1984 300cd

[drmathieu]

My 1984 300cd has been garage kept since last fall. I have 303,000K miles on the car. I needed to replace the two rear axles. I was hearing a noise in the rear but the car was also very slow off the start and would be very slow going up hills. I would lose 10+ mph (up hills) with the gas pedal push to the floor. I was thinking that the noise was due to the CV joints and the sluggish driving was a result of the CV's also. After having the CV joints replaced, the noise has stopped but the performance of the vehicle is still the same.

I have also replaced both the primary and in line fuel filters.

I was just wondering if anyone would help to point me in a new direction?
Could it be wheel bearings? transmission? turbo?

Thank you in advance for your time.