Mysterious force holding the car back: slower acceleration, lower mileage. brake????

[wawago]

Hi, I have an 87 560SEL. Recently (1month) I feel the car accelerates noticeable slower than before. Another person feels it too without me telling her the problem in the first place. It feels like when you press on the gas paddle and you wonder why the car is (about 20%) slower. But he engine feels as strong as before. In other words, it feels like something like the brakes are holding the car back. In addition the gas mileage is lower too. Everything else feels normal: brake power, engine power, fluid level, parking brake, etc. This problem seemed to first start after I put in a new front parking brake cable. But I am not quiet sure because during that time I also changed the brake fluid, A/T fuid, P/S fluid and Diff. oil all with MB spec.

I have checked and readjusted my parking brake according to MB manual: release parking brake, loosen parking brake adjuster, tighten parking brake until the wheel can't spin freely, then back off 4-5 clicks, tighten the adjuster until no cable slack, press/release parking brake several times, and retighten the adjuster until 120N (don't quite remember) is required to press the parking brake 1 click. Both front wheels spin freely about 2 rotations per spin by hand. Where as both the rear wheels spin only about 1 rotation per spin. I have compared them to my 88 300ce they seem to be about the same.

I really don't know what to look for to solve this problem. You help will be greatly appreciated.

Thanks

Rick