Many thanks for responding. I am sched'd tomorrow for round two at the mechanic.
As for the questions posed to me: It appears to be narrowly confined to the stated rpms at the stated speeds. I have carefully observed rpms @ 1800-2000 at lower/higher speeds and higher rpms while accelerating faster thru 45-60. The typical episode goes like this: upon shifting into the higher gear/overdrive(mech's suggestion btw), the rpms naturally drop to 1800 before settling in at 2000 and slightly above. This is accompanied by the stated shudder. Should I relieve pressure upon the accelerator the shudder vanishes. The rpms may drop from 2500 back down to 1800 during this coasting maneuver. Touching the accelerator provokes a strong shudder, clearly felt through my right foot enough to shake my leg. I would describe this shudder as having a low end frequency but high amplitude in the range of motion and rapidly thereof seen in this phenom.
I'm no mechanic but seems to me that tires would provide a constant effect with no relief while coasting, although perhaps the front wheel drive could be involved if the tires were to at fault. While in park, neutral, or idle there is no shudder at any rpm.
Torque converter is something I will ask about to be sure, as to me it almost feels like the exhaust pipes (or something akin to that shape) under the car is wobbling violently. Could that be it I wonder (tc)? I also wonder about the possibility that a motor mount is cracked or fractured in such a way as to be not noticed as yet. I still wonder if a fuel injector could be off enough to cause the engine to go so out of sync as to shake and rattle while I roll on.
I'll let the pros handle the problem but I shall ask if I'm not satisfied with what I hear (or feel).
Thanks again. I'll let y'all know how it goes.-Oscar