'97 Burb whine (need input from all)

I have a '97 Suburban K1500 with a 5.7. About a year ago on a trip pulling my camper (weighs about 5,000#'s) my truck started making a whine. The noise happens at about 1,500 rpm in D or OD. It gets a
little louder when the converter locks up. It seems to be the loudest when I press the accelerator just so I am barely decreasing speed. If I just maintain speed, the noise is not as loud or if I accelerate or completely let off pedal the noise goes away. The noise is not always at the same volume and it does not matter if I am pulling a load or not. Since the noise started I have replaced the following (none for the noise reason): engine completely rebuilt, trans completely rebuilt (replaced torque converter, sun shell and all other usual parts, planetary gears spun smoothly), and had new gears and bearings put in rear end (wanted 4:10 for pulling, man what a difference). The engine and trans were rebuilt by well qualified and highly recommended independent mechanics. The same person did the rear end and trans in that order. When he rebuilt the rear end and test drove it he thought it might be the torque converter. I have about 10,000 miles on engine and trans (I pulled both at same time and had both rebuilt). About 6,000 of those miles were pulling my camper (went cross country). After the trip I changed trans fluid. It was just as clean as the day I poured it in. No dust or any material in trans pan. The noise is not something I want to spend a $1,000 on trying to diagnose. It is a nuisance, but not something that will stop me from driving the truck. Since the noise started, it has never gotten any worse. It came on suddenly and has been fairly consistant ever since.
All input will be greatly appreciated,

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