Tranny Slipping? Maybe???

[goclmbmnt]

Okay, I have a strange problem. First of all, I have a 2001 Chevy Suburban, 3/4 ton, with the 8.1L in it. Not sure of the transmission type/number. About 100,000 miles with every recommended service being performed, usually at the dealer.

When I am going faster than 45 mph down hill and let my foot off the gas and begin to coast, as is normally the case, the engine starts to slow down the rig. After a second or two, I get a load whirling noise that seems to be coming from the transmission and the RPMs drop to idle, even though I am in gear and traveling 45+ mph. To clear the issue I can slow to about 30 or press the gas and almost "engage" the tranny again. It doesn't matter if I am in overdrive, or have downshifted. It really seems that the tranny or torque converter slips when enough pressure is put onto the system. But I don't understand the mechanics of how each operate, so it might be something else?

Note that it only has a problem when I'm slowing. Performs great otherwise, no slipping and I pull a 8,000 lbs boat with it.

I ignored it after it happened the first time 18 months ago. After it happened again, I took it into the dealer who said there are no codes in the transmission. They did a filter and flush of the tranny fluid and sent me on my way. Since then, it has slowly become more frequent.

Any helps or suggestions? It's going back into a tranny shop as soon as I get my other car out of the shop, but I'm worried they won't find anything wrong. I'd love to be able to suggest a starting point or two.

Thanks in advance.

[Joeairforce]

Sounds like maybe the Torque Converter Clutch is unlocking to me. Might need a new lock-up solenoid....