Bizarre symptoms E300TD update

After implementing many of the suggestions offered here, I was able to get
my 99E300TD back on the road. Replacement of the O-rings and the pre filter
and main filter got all the air bubbles out of the system. While in the shop,
a bad alternator was found to be the cause of both the "battery charge" warning that came on intermittently and rapid wear on the belt tensioner shock. All was great EXCEPT now the car misses periodically at idle only in neutral or park. Shift to D or R and it idles normally. Accelleration and cruise
is normal as is fuel consumption. Now the car is in a different shop in a different city for the third day while a further diagnosis is being attempted.
This shop thinks it is an electrical problem since it idles normally when the lights are turned on or when the Compressor is engaged. I suggested that this simply is putting load on the drive belt much as shifting into gear is especially since no electrical problems have popped up. Injectors have been ruled out as have the ECM and the injector pump(how, I don't know).

Anyone got an idea?

Steve