[T3] Distributer placement/Timing

[rheorojo@F]

Is this an issue (improperly seated distributor)that would result in the timing drifting out within 50-100 miles? I've had a similar issue where, I time the car (73 sqbk auto) and within 50-100 miles it's out buy 4-5 degrees. The distributer clamp was deformed some so I have replaced it. I have installed 2 different distributers (both the correct ones, one rebuilt buy Jim), and experience the same issue. I changed the rotor to some measure of improvement (very little) but it still drifts. I have installed an electronic ignition for the same result. I have observed the timing to be very steady at idle, but when I run the rpm's up and hold it constant the timing tends to drift (i'm guessing 5-7 degrees) like there is some slop in the gears, or an intermittent electric signal. This motor has less than 5000 miles since a complete rebuild. I'll check the distributer tonight, but it felt like it hit home when I installed it. I had the rebuild due to poor mileage and an oil leak. (20 mpg, when previously it was in the upper 20's low 30's) 
Tim