Timing mark jumps, bad milage

[craphandler13]

I have a 92 sierra with the 4.8. With the tan/black wire connected, the timing mark jumps all over the place when seen with a timing light. With the wire disconnected, the mark sits at zero. I did notice that the rotor has play so i am changing the distributer gear. Also when cold, the engine has very little power upon acceleration. Seems ok when warm. I also noticed that the interior part of the coil is a little loose(wiggles independently of the outer part). Could this cause the problem? It also gets poor fuel mileage(about 250 miles to a tank city driving) It has a 25 gallon tank. Changed plugs, cap, rotor, wires. Any help would be appreciated.