Ok, i'm no technician but this morning when i was on my way to work, i pulled up to a stoplight and when it turned green, i put the pedal at about half or 1/3 throttle, and the whole dash rattled and shook at about 1500-2000 rpm, then went away, and came back on when the car downshifted on the freeway from 4th to 3rd at about 45mph. I can duplicate this anytime i am in 4th gear and mildly accelerating from 35mph up past 40. It occurs in more than one gear, and happens under part throttle. Any ideas about what is up? Is it a fuel problem? it doesn't feel like a miss, and when the car is not in gear, and i slowly rev it up, there is no sign of a miss. I popped the hood in the parking lot and nothign seemed out of sorts. it almost feels like spark knock, but it goes away under full throttle, it is only at part throttle. Could it be a tranny problem? Maybe the lock up convertor? I am putting this on both the tbi and tranny boards, as i don't know which it could be related to.
Any help would be greatly appreciated. My gut reaction is that it feels like a torque convertor lockup problem causing some sort of spark knock, but i dont' know, is there anyway i can disable the lockup easily in my driveway, so i could drive it and test it with/without the lockup? Or do i have to have the lockup on for the tranny to work right?

thanks,
Mike