Back again looking for some diagnostic advice. The victim is an '88 744 with the B230F and AW tranny. She currently has about 175k miles.

About 5-6 weeks ago I found a leak in the radiator as I was pulling into my driveway. Not a big leak and no overheating happened. I parked the car until this past weekend when I finally had time to install a new radiator. Purchased an all metal 3-row unit online and the install went well. Pretty easy actually, even for being the first time I've done such a thing.

Replaced the upper and lower hoses while I was at it as a preventative measure. When I was done, I filled up with water/antifreeze, checked the AT fluid and the car was running fine and no leaks. Oddly, the dipstick showed that it did not need any AT fluid. Drove it around the neighborhood to get her good and warmed up, water level just fine and still the AT fluid was still showing full.

I drove it to work Monday and Tuesday (~25mi one way) and have noticed a low rumble and vibration in the driveline. It is worst when under power, but you can just barely feel something when put in gear. It seemed to be worse on Tuesday than Monday. The car still drives fine, has plenty of power, and changes gears as normal despite this affliction. I've parked it again until I can figure out what to look for. This is where I need some help.

My concerns center around two areas: transmission and driveline (shaft). The fact that it does not need ATF makes me wonder if the fluid is not circulating through the radiator. Could it be airlocked or blocked? If so, would it cause this sort of problem? Having set for a couple of weeks I can't imagine this would be the case, but I am also thinking the u-joints and/or center driveshaft bearing might be bad. (both original with the car, BTW) I can get under the car this weekend and check the driveshaft stuff, but not so sure about the transmission.

Any thoughts? TIA.
Landon