2000 Silverado torque converter shudder. - Hello All, I am new to this forum and hope you can help me here. I also look fwd to being able to contribute ...

Hello All, I am new to this forum and hope you can help me here. I also look fwd to being able to contribute on other issues. so here it is.

Issue surfaced after trans broke and was replaced. Trans replaced, torque converter shudders between 40 and 50 when applying throttle but not enough to down shift. Shop replaced converter 3 different times, went completely back thru trans again, shudder still there. Replaced PCM at dealer after multiple test drives revealed no issues with Tech 2 hooked up, no DTC's, no malfunctions anywhere to be found. Duty cycle during TC lock up and unlock is normal. TPS was replaced but revealed no change. Light application of brake while driving shows converter lock up functions correctly. Lube Guard added, no change. Trans Shop will not do anything further at this point as they are positive it's not the trans. 2 shops I've taken it to, after multiple hrs trying to diagnose it are convinced it is the trans. Do I start throwing parts at it in hopes I can locate the culprit that's commanding the trans to act like this? I have a difficult time accepting this is a coincidence issue that appeared when original trans broke but I have seen weirder stuff before. Truck drove and ran fantastic prior to trans breaking. Tune up parts have approx 30K on them. I use OEM parts only. Please help, I am at point of trading in truck.
Truck is a 2000 Silverado, 2WD, 5.3, 4L60E, stock. My wife says trade it in and get a new Avalanche however, I really like this truck and it's condition is not far off new. Owned it 7 yrs, kept it immaculate.

UPDATE....... Plugs and wires replaced, added LubeGuard to trans. Much improvement. Still feel a slight shudder but MUCH improved. Has anyone else encountered this type of issue?